Photosensitive composition

ABSTRACT

A photosensitive composition comprising: a sensitizing dye represented by the following formula (1): 
                         
in which A represents an optionally substituted aromatic ring or an optionally substituted hetero ring; X represents an oxygen atoms a sulfur atom, or —N(R 6 )—; and R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  each independently represents a hydrogen atom or a monovalent non-metal atomic group; an activator compound being capable of causing a chemical change due to a mutual action with light absorption of the sensitizing dye represented by the formula (1) so as to generate at least one of a radical, an acid and a base; and a compound being capable of reacting with at least one of a radical and an acid so that physical or chemical characteristics thereof change irreversibly.

FIELD OF THE INVENTION

The present invention relates to a novel sensitizing dye and aphotosensitive composition containing a photoinitiation system using thesensitizing dye, especially a photoinitiation system having highsensitivity and excellent stability. Also, the invention relates to aphotosensitive composition (photopolymerizable composition) which isexcellent as a material for lithographic printing plate precursorcapable of being subjected to plate making by scan exposure on a basisof digital signals.

BACKGROUND OF THE INVENTION

Hitherto, a PS plate having a construction wherein a lipophilicphotosensitive resin layer is provided on a hydrophilic support has beenwidely used as a lithographic printing plate. With respect to the platemaking method thereof, in general, a desired printing plate has beenobtained by mask exposure (surface exposure) via a lith film anddissolution and removal of a non-image area.

In recent years, the digitalizing technology for electronic processing,accumulating and outputting of image information by using a computer hasbecome widespread, and a variety of new image outputting systemscorresponding thereto have been put into practical use. As a result, thecomputer-to-plate (CTP) technology for scanning light having highdirectivity such as laser beam according to digitalized imageinformation and directly producing a printing plate without using a lithfilm is desired, and it is an important technical problem to obtain aprinting plate precursor adaptive therewith.

As one of systems for obtaining a lithographic printing plate which canbe subjected to scan exposure, a construction wherein aphotopolymerization based composition having excellent photosensitivespeed is used in an ink-receptive photosensitive resin layer(hereinafter referred to as “photosensitive layer”) to be provided on ahydrophilic support has hitherto been proposed and already marketed. Aprecursor having such a construction bas desired printing performancesuch that not only it is simple in development treatment, but also it isexcellent in resolution, inking properties, printing resistance, andstaining resistance.

The foregoing photopolymerizable composition is basically composed of anethylenically unsaturated compound, a photopolymerization initiationsystem, and a binder resin, and the image formation is achieved by thematter that the photoinitiation system absorbs light to generate anactive radical and cause addition polymerization of the ethylenicallyunsaturated compound, thereby insolubilizing the photosensitive layer.

The majority of conventional proposals regarding a photopolymerizablecomposition capable of being subjected to scan exposure disclose the useof a photoinitiation system excellent in photosensitivity and aredescribed in, for example, Bruce M. Monroe, et al., Chemical Revue, Vol.93 (1993), pp. 435-448, and R. S. Davidson, Journal of Photochemistryand Biology A: Chemistry, Vol. 73 (1993), pp. 81-96.

With respect to a conventional CTP system using a photopolymerizablecomposition composed of such an initiation system and a visible lightsource having a long wavelength such as Ar laser (488 nm) and FD-YAGlaser (532 nm) as a light source, for the sake of enhancing productivityof the plate making step, it is desired to undergo writing at a higherspeed. However, its object has not been achieved yet because an outputof the light source is not sufficiently high and sensitivity of thephotographic material is not sufficiently high.

On the other hand, in recent years, for example, semiconductor laserwhich can undergo continuous oscillation in a region of from 350 nm to450 nm by using an InGaN based material is in the stage of practicaluse. In a scan exposure system using such a short wavelength lightsource, since the semiconductor laser can be cheaply produced from thestructural standpoint, it has an advantage that while it has asufficient output, an economical system can be constructed. In addition,it is possible to use a photographic material, the photosensitive regionof which is present in a short wave side and which can be worked under abrighter safe light, as compared with the conventional system usingFD-YAG or Ar laser.

However, a photoinitiation system having sufficient sensitivity againstscan exposure in a short wavelength region of from 350 nm to 450 nm hasnot been known up to date.

Additionally, what a photoinitiation system having high sensitivity isobtained is a more earnestly desired technology widely in the imagingfield (for example, see JP-A-2000-258910, J. P. Faussier, PhotoinitiatedPolymerization-Theory and Applications: Rapra Review., Vol. 9, Report,Rapra Technology (1998), and M. Tsunooka, et al., Prog. Polym. Sci., 21,1 (1996)). A photoinitiation system composed of a sensitizing dye and anactivator can generate an acid or a base in addition to the foregoingactive radical by choosing the activator. For example, such aphotoinitiation system is utilized for the image formation such asoptical fabrication, holography, and color hard copying, the fabricationfield of electronic materials such as photoresists, and photo-curableresin materials such as inks, paints, and adhesives. In these industrialfields, for the sake of causing decomposition of the activator with goodefficiency, it is eagerly desired to find out a sensitizing dye havingexcellent light absorptivity and sensitizing ability.

SUMMARY OF THE INVENTION

An object of the invention is to provide a photosensitive compositionwith high sensitivity and, when the subject photosensitive compositionis, for example, used for a lithographic printing plate precursor, toprovide a photosensitive composition from which a lithographic printingplate precursor which is high in sensitivity, can be handled even undera bright safe light and is excellent in printing resistance and stainingresistance even under a scan exposure condition with very low energy(for example, scan exposure using a laser light source having a shortwavelength of from 350 to 450 nm) can be obtained.

In order to achieve the foregoing object, the present inventors madeextensive and intensive investigations. As a result, it has been foundthat a novel photoinitiation system comprising a novel sensitizing dyehaving a specific structure and an activator as a polymerizationinitiator gives especially high photosensitivity, leading toaccomplishment of the invention.

Specifically, the invention is as follows.

-   (1) A Photosensitive Composition Containing:

(i) a sensitizing dye represented by the following formula (1),

(ii) an activator compound being capable of causing a chemical changedue to a mutual action with light absorption of the sensitizing dyerepresented by the formula (1), thereby generating at least one of aradical, an acid, and a base, and

(iii) a compound being capable of reacting with at least one of aradical and an acid, whereby physical or chemical characteristicsthereof change irreversibly.

In the formula (1), A represents an optionally substituted aromatic ringor hetero ring; X represents an oxygen atom, a sulfur atom, or —N(R₆)—;and R₁, R₂, R₃, R₄, R₅, and R₆ each independently represents a hydrogenatom or a monovalent non-metal atomic group.

-   (2) The photosensitive composition as set forth above in (1),    wherein the activator compound is at least one titanocene compound.-   (3) The photosensitive composition as set-forth above in (1) or (2),    wherein the compound being capable of reacting with at least one of    a radical and an acid, whereby physical or chemical characteristics    thereof change irreversibly is an addition polymerizable compound    having an ethylenically unsaturated double bond.

The compound represented by the formula (1) has a large mutual actionbetween the electron excited state as generated by light absorption andthe activator compound and has a function to effectively decompose theactivator compound, and therefore, the photosensitive compositioncontaining the subject compound becomes high in sensitivity.Accordingly, in the case of using this composition in a photosensitivelayer, it is possible to provide a lithographic printing plate precursorwith high sensitivity even under a scan exposure condition of very lowenergy (for example, scan exposure using a laser light source having awavelength shorter than 450 nm). Furthermore, a lithographic printingplate precursor having the photosensitive composition of the inventionin a photosensitive layer thereof can be handled even under a brightsafe light and is excellent in printing resistance and stainingresistance.

DETAILED DESCRIPTION OF TH INVENTION

Embodiments of the invention will be described below in detail.

(A. Photoinitiation System)

A photoinitiation system of the invention comprises (i) a sensitizingdye having a specific structure represented by the formula (1) and (ii)an activator compound which is capable of causing a chemical change dueto a mutual action with the electron excited state as generated by lightabsorption of the subject sensitizing dye, thereby generating at leastone of a radical, an acid, and a base.

One of the characteristic features of the sensitizing dye (i) of theinvention resides in the matter that it has especially excellentabsorption characteristics in a region of from 350 nm to 450 nm.Furthermore, the sensitizing dye (i) causes decomposition of a varietyof activator compounds with good efficiency, thereby exhibiting veryhigh photosensitivity. In general, it is known that a sensitizationmechanism of a photoinitiation system comprising a sensitizing dye andan activator compound takes a route such as (1) reductive decompositionof the activator compound on a basis of an electron transfer reactionfrom the electron excited state of the sensitizing dye to the activatorcompound, (2) oxidative decomposition of the activator compound on abasis of electron transfer from the activator compound to the electronexcited state of the sensitizing dye, and (3) decomposition from theelectron excited state of the activator compound on a basis of energytransfer from the electron excited state of the sensitizing dye to theactivator compound. It has been noted that the sensitizing dye of theinvention causes the sensitization reaction of any of these types withexcellent efficiency.

The present inventors have found that the compound represented by theformula (1) exhibits high sensitivity as a sensitizing dye. The reasonwhy the specific structure represented by the formula (1) is a veryimportant factor in enhancing the sensitivity is not completelyelucidated yet. However, since it exhibits an emission (fluorescenceand/or phosphorescence) spectrum with high intensity, it may beconsidered as one possibility that the sensitizing dye of the inventionhas a relatively long excitation life and acts to make reaction with theactivator compound efficient. Furthermore, it has become clear that bycontaining a substituent such as an alkoxy group, an aryloxy group, andan oxycarbonyl group, the sensitizing dye of the invention canremarkably enhance suppression of the deposition of crystal at the timeof storage, i.e., storage stability. Though its factor is not completelyelucidated yet, it may be considered that by containing a substituenthaving high polarity, compatibility in the photosensitive compositionlayer is enhanced, whereby such a function acts.

(A1) Sensitizing Dye:

The sensitizing dye which is used in the invention is a compoundrepresented by the following formula (1)

In the formula (1), A represents an optionally substituted aromatic ringor hetero ring; X represents an oxygen atom, a sulfur atom, or —N(R₆)—;and R₁, R₂, R₃, R₄, R₅, and R₆ each independently represents a hydrogenatom or a monovalent non-metal atomic group.

The formula (1) will be described below in detail.

The monovalent non-metal atomic group represented by R₁, R₂, R₃, R₄, R₅,and R₆ (hereinafter sometimes abbreviated as “R₁ to R₆”) preferablyrepresents a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted aryl group,a substituted or unsubstituted aromatic heterocyclic group, asubstituted or unsubstituted alkynyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted alkylthiogroup, a hydroxyl group, an acyl group, a substituted or unsubstitutedalkoxycarbonyl group, a substituted or unsubstituted aryloxycarbonylgroup, a halogen atom, an aryloxy group, an arylthio group, or anN,N-dialkylamino group.

Preferred examples of R₁ to R₆ will be specifically described below.

Preferred examples of the alkyl group include linear, branched or cyclicalkyl groups having from 1 to 20 carbon atoms. Specific examples thereofinclude a methyl group, an ethyl group, a propyl group, a butyl group, apentyl group, a hexyl group, a heptyl group, an octyl group, a nonylgroup, a decyl group, an undecyl group, a dodecyl group, a tridecylgroup, a hexadecyl group, an octadecyl group, an eicosyl group, anisopropyl group, an isobutyl group, a sec-butyl group, a t-butyl group,an isopentyl group, a neopentyl group, a 1-methylbutyl group, anisohexyl group, a 2-ethylhexyl group, a 2-methylhexyl group, acyclohexyl group, a cyclopentyl group, and a 2-norbornyl group. Ofthese, liner alkyl groups having from 1 to 12 carbon atoms, branchedalkyl groups having from 3 to 12 carbon atoms, and cyclic alkyl groupshaving from 5 to 10 carbon atoms are more preferable.

As a substituent of the substituted alkyl group, a monovalent non-metalatomic group other than hydrogen is used. Preferred examples thereofinclude a halogen atom (for example —F, —Br, —Cl, and —I), a hydroxylgroup, an alkoxy group, an aryloxy group, a mercapto group, an alkylthiogroup, an arylthio group, an alkyldithio group, an aryldithio group, anamino group, an N-alkylamino group, an N,N-alkylamino group, anN-arylamino group, an N,N-diarylamino group, an N-alkyl-N-arylaminogroup, an acyloxy group, a carbamoyloxy group, an N-alkylcarbamoyloxygroup, an N-arylcarbamoyloxy group, an N,N-dialkylcarbamoyloxy group, anN,N-diaryl-carbamoyloxy group, an N-alkyl-N-arylcarbamoyloxy group, analkylsulfoxy group, an arylsulfoxy group, an acylthio group, anacylamino group, an N-alkylacylamino group, an N-arylacylamino group, anureido group, an N′-alkylureido group, an N′,N′-dialkylureido group, anN′-arylureido group, an N′,N′-diarylureido group, anN′-alkyl-N′-arylureido group, an N-alkylureido group, an N-arylureidogroup, an N′-alkyl-N-alkylureido group, an N′-alkyl-N-arylureido group,an N′,N′-dialkyl-N-alkylureido group, an N′,N′-dialkyl-N-arylureidogroup, an N′-aryl-N-alkylureido group, an N′-aryl-N-arylureido group, anN′,N′-diaryl-N-alkylureido group, an N′,N′-diaryl-N-arylureido group, anN′-alkyl-N′-aryl-N-alkylureido group, an N′-alkyl-N′-aryl-N-arylureidogroup, an alkoxycarbonylamino group, an aryloxycarbonylamino group, anN-alkyl-N-alkoxycarbonylamino group, an N-alkyl-N-aryloxycarbonylaminogroup, an N-aryl-N-alkoxycarbonylamino group, anN-aryl-N-aryloxycarbonylamino group, a formyl group, an acyl group, acarboxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, acarbamoyl group, an N-alkylcarbamoyl group, an N,N-dialkylcarbamoylgroup, an N-arylcarbamoyl group, an N,N-diarylcarbamoyl group, anN-alkyl-N-arylcarbamoyl group, an alkylsulfinyl group, an arylsulfinylgroup, an alkylsulfonyl group, an arylsulfonyl group, a sulfo group(—SO₃H) and its conjugated base group (hereinafter referred to as“sulfonato group”), an alkoxysulfonyl group, an aryloxysulfonyl group, asulfinamoyl group, an N-alkylsulfinamoyl group, an N,N-dialkysulfinamoylgroup, an N-arylsulfinamoyl group, an N,N-diarylsulfinamoyl group, anN-alkyl-N-arylsulfinamoyl group, a sulfamoyl group, an N-alkylsulfamoylgroup, an N,N-dialkylsulfamoyl group, an N-arylsulfamoyl group, anN,N-diarylsulfamoyl group, an N-alkyl-N-arylsulfamoyl group, a phosphonogroup (—PO₃H₂) and its conjugated base group (hereinafter referred to as“phosphonato group”), a dialkylphosphono group (—PO₃(alkyl)₂), adiarylphosphono group (—PO₃(aryl)₂), an alkylarylphosphono group(—PO₃(alkyl)(aryl)), a monoalkylphosphono group (—PO₃—H(alkyl)) and itsconjugated base group (hereinafter referred to as “alkylphosphonatogroup”), a monoarylphosphono group (—PO₃H(aryl)) and its conjugated basegroup (hereinafter referred to as “arylphosphonato group”), aphosphonooxy group (—OPO₃H₂) and its conjugated base group (hereinafterreferred to as “phosphonatooxy group”), a dialkylphosphonooxy group(—OPO₃(alkyl)₂), a diarylphosphonooxy group (—OPO₃(aryl)₂), analkylarylphosphonooxy group (—OPO₃(alkyl)(aryl)), amonoalkylphosphonooxy group (—OPO₃H(alkyl)) and its conjugated basegroup (hereinafter referred to as “alkylphosphonatooxy group”), amonoarylphosphonooxy group (—OPO₃H(aryl)) and its conjugated base group(hereinafter referred to as “aryl-phosphonatooxy group”), a cyano group,a nitro group, an aryl group, a heteroaryl group, an alkenyl group, andan alkynyl group.

In these substituents, as specific examples of the alkyl group, theforegoing alkyl groups can be enumerated. Specific examples of the arylgroup include a phenyl group, a biphenyl group, a naphthyl group, atolyl group, a xylyl group, a mesityl group, a cumenyl group, achlorophenyl group, a bromophenyl group, a chloromethylphenyl group, ahydroxyphenyl group, a methoxyphenyl group, an ethoxyphenyl group, aphenoxyphenyl group, an acetoxyphenyl group, a benzoyloxyphenyl group, amethylthiophenyl group, a phenylthiophenyl group, a methylaminophenylgroup, a dimethylaminophenyl group, an acetylaminophenyl group, acarboxyphenyl group, a methoxycarbonylphenyl group, anethoxyphenylcarbonyl group, a phenoxycarbonylphenyl group, anN-phenylcarbamoylphenyl group, a phenyl group, a cyanophenyl group, asulfophenyl group, a sulfonatophenyl group, a phosphonophenyl group, anda phosphonatophenyl group.

As the aromatic heterocyclic group which is preferred as R₁ to R₆ amonocyclic or polycyclic aromatic ring containing at least one ofnitrogen, oxygen, and sulfur atoms is used. Examples of the aromaticheterocyclic ring which is especially preferable include thiophene,thianthrene, furan, pyran, isobenzofuran, chromene, xanthene,phenoxazine, pyrrole, pyrazole, isothiazole, isoxazole, pyrazine,pyrimidine, pyridazine, indolizine, isoindolizine, indoyl, indazole,purine, quinolizine, isoquinoline, phthalazine, naphthylidine,quinazoline, cinoline, pteridine, carbazole, carboline, phenanthrene,acridine, perimidine, phenanthroline, phthalazine, phenarsazine,phenoxazine, furazane, and phenoxazine. These may be further benzo-fusedor may have a substituent.

Furthermore, examples of the alkenyl group which is preferred as R₁ toR₆ include a vinyl group, a 1-propenyl group, a 1-butenyl group, acinnamyl group, and a 2-chloro-1-ethenyl group; and examples of thealkynyl group include an ethynyl group, a 1-propynyl group, a 1-butynylgroup, and a trimethylsilylethynyl group. Examples of G1 in the acylgroup (G1CO—) include hydrogen and the foregoing alkyl groups and arylgroups.

On the other hand, as the alkylene group on the substituted alkyl group,there are enumerated divalent organic residues resulting fromelimination of any one of hydrogen atoms on the foregoing alkyl grouphaving from 1 to 20 carbon atoms. Of these, linear alkylene groupshaving from 1 to 12 carbon atoms, branched alkylene groups having from 3to 12 carbon atoms, and cyclic alkylene groups having from 5 to 10carbon atoms are preferable.

Specific examples of the substituted alkyl group which is preferred asR₁ to R₆ and which is obtained by combining the subject substituent withthe alkylene group include a chloromethyl group, a bromomethyl group, a2-chloroethyl group, a tri-fluoromethyl group, a methoxymethyl group, arnethoxyethoxyethyl group, an allyloxymethyl group, a phenoxymethylgroup, a methylthiomethyl group, a tolylthiomethyl group, anethylaminoethyl group, a diethylaminopropyl group, a morpholinopropylgroup, an acetyloxymethyl group, a benzoyloxymethyl group, anN-cyclobexylcarbamoyloxyethyl group, an N-phenylcarbamoyloxyethyl group,an acetylaminoethyl group, an N-methylbenzoylaminopropyl group, a2-oxoethyl group, a 2-oxopropyl group, a carboxypropyl group, amethoxycarbonylethyl group, an allyloxycarbonylbutyl group, achlorophenoxycarbonylmethyl group, a carbamoylmethyl group, anN-methylcarbamoylethyl group, an N,N-dipropylcarbamoylmethyl group, anN-methoxyphenyl)carbamoylethyl group, anN-methyl-N-(sulfophenyl)carbamoylmethyl group, a sulfobutyl group, asulfonatobutyl group, a sulfamoylbutyl group, an N-ethylsulfamoylmethylgroup, an N,N-dipropyl-sulfamoylpropyl group, an N-tolylsulfamoylpropylgroup, an N-methyl-N-(phosphono-phenyl)sulfamoyloctyl group, aphosphonobutyl group, a phosphonatohexyl group, a diethylphosphonobutylgroup, a diphenylphosphonopropyl group, a methyl-phosphonobutyl group, amethylphosphonatobutyl group, a tolylphosphonohexyl group, atolylphosphonatohexyl group, a phosphonoxypropyl group, aphosphonatoxybutyl group, a benzyl group, a phenethyl group, anα-methylbenzyl group, a 1-methyl-1-phenylethyl group, a p-methylbenzylgroup, a cinnamyl group, an allyl group, a 1-propenylmethyl group, a2-butenyl group, a 2-methylallyl group, a 2-methylpropenylmethyl group,a 2-propynyl group, a 2-butynyl group, and a 3-butynyl group.

Moreover, specific examples of the aryl group which is preferred as R₁to R₆ include ones resulting from the formation of a fused ring of fromone to three benzene rings and ones resulting from the formation of afused ring of a benzene ring and a 5-membered unsaturated ring. Specificexamples thereof include a phenyl group, a naphthyl group, an anthrylgroup, a phenanthryl group, an indenyl group, an acenaphthenyl group,and a fluorenyl group. Of these, a phenyl group and a naphthyl group aremore preferable.

Specific examples of the substituted aryl group which is preferred as R₁to R₆ include ones having a monovalent non-metal atomic group other thanhydrogen as the substituent on the ring-forming carbon atoms of theforegoing aryl group. Examples of the preferred substituent include theforegoing alkyl groups and substituted alkyl groups and those asenumerated as the substituent in the foregoing substituted alkyl group.Preferred examples of such substituted aryl groups include a biphenylgroup, a tolyl group, a xylyl group, a mesityl group, a cumenyl group, achlorophenyl group, a bromophenyl group, a fluorophenyl group, achloromethylphenyl group, a tri-fluoromethylphenyl group, ahydroxyphenyl group, a methoxyphenyl group, a methoxyethoxyphenyl group,an allyloxyphenyl group, a phenoxyphenyl group, a methylthiophenylgroup, a tolylthiophenyl group, an ethylaminophenyl group, adi-ethylaminophenyl group, a morpholinophenyl group, an acetyloxyphenylgroup, a benzoyloxyphenyl group, an N-cyclohexylcarbamoyloxyphenylgroup, an N-phenylcarbamoyloxyphenyl group, an acetylaminophenyl group,an N-methylbenzo-ylaminophenyl group, a carboxyphenyl group, amethoxycarbonylphenyl group, an allyloxycarbonylphenyl group, achlorophenoxycarbonylphenyl group, a carbamoylphenyl group, anN-methylcarbamoylphenyl group, an N,N-dipropylcarbamoylphenyl group, anN-(methoxyphenyl)carbamoylphenyl group; anN-methyl-N-(sulfophenyl)carbamoylphenyl group, a sulfophenyl group, asulfonatophenyl group, a sulfamoylphenyl group, anN-ethylsulfamoylphenyl group, an N,N-dipropylsulfamoylphenyl group, anN-tolylsulfamoylphenyl group, anN-meth-yl-N-(phosphonophenyl)sulfamoylphenyl group, a phosphonophenylgroup, a phosphonatophenyl group, a diethylphosphonophenyl group, adiphenylphosphonophenyl group, a methylphosphonophenyl group, amethylphosphonatophenyl group, a tolylphosphonophenyl group, atolylphosphonatophenyl group, an allyl group, a 1-propenylmethyl group,a 2-butenyl group, a 2-methylallylphenyl group, a 2-methylpropenylphenylgroup, a 2-propynylphenyl group, a 2-butynylphenyl group, a3-butynylphenyl group, and an N,N′-diphenylaminophenyl group.

Furthermore, specific examples of the substituted or unsubstitutedalkoxy group which is preferred as R₁ to R₆ include a methoxy group, anethoxy group, a butoxy group, a hexyloxy group, a 2-ethylhexyloxy group,a cyclohexyloxy group, and an isopropyloxy group.

Specific examples of the substituted or unsubstituted alkylthio groupwhich is preferred as R₁ to R₆ include a methylthio group, an ethylthiogroup, a butylthio group, a hexylthio group, a 2-ethylhexylthio group, acyclohexylthio group, and an isopropylthio group.

Specific examples of the substituted or unsubstituted alkoxycarbonylgroup which is preferred as R₁ to R₆ include a methoxycarbonyl group, anethoxycarbonyl group, a butoxycarbonyl group, a hexyloxycarbonyl group,a 2-ethylhexyloxycarbonyl group, a cyclohexyloxycarbonyl group, and anisopropyloxycarbonyl group.

Specific examples of the substituted or unsubstituted aryloxycarbonylgroup which is preferred as R₁ to R₆ include a phenoxycarbonyl group, anacetoxyphenoxycarbonyl group, a methoxyphenoxycarbonyl group, acyanophenoxycarbonyl group, a dimethylaminophenoxycarbonyl group, and adiphenylaminophenoxycarbonyl group.

As more preferred examples as R₁ to R₆, a hydrogen atom, a halogen atom(for example, —F, —Br, —Cl, and —I), an alkoxy group, an aryloxy group,an alkylthio group, an arylthio group, an N,N-dialkylamino group, anacyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an arylgroup, and an alkenyl group are enumerated.

As especially preferred examples as R₁ to R₆, a hydrogen atom, asubstituted or unsubstituted alkyl group, and a substituted orunsubstituted alkoxy group are enumerated.

Next, A in the formula (1) will be described. A represents an optionallysubstituted aromatic ring or hetero ring. Specific examples of theoptionally substituted aromatic ring or hetero ring include those whichare the same as described for R₁ to R₆ in the formula (1). As especiallypreferred examples of A, an optionally substitutedN,N-diphenylaminobenzene group and an optionally substituted carbazolegroup are enumerated.

Next, X in the formula (1) will be described. X represents an oxygenatom, a sulfur atom, or —N(R₆)—. Preferred examples of R₆ are the sameas described previously. As a more preferred example of X, an oxygenatom is enumerated.

The sensitizing dye represented by the formula (1) of the invention isobtained by condensation reaction of an active methylenegroup-containing acidic nucleus with a substituted or unsubstitutedaromatic ring or hetero ring and can be synthesized by referring toJP-B-59-28329.

Specific examples (D1) to (D31) which are preferable as the compoundrepresented by the formula (1) will be given below, but it should not beconstrued that the invention is limited thereto. Furthermore, isomersdue to a double bond which binds an acidic nucleus to a basic nucleusare not completely elucidated yet, and the invention is never limited toeither one isomer.

With respect to the sensitizing dye of the invention, it is possible tofurther carry out a variety of chemical modifications for the purpose ofimproving characteristics of the photosensitive layer. For example, whenthe sensitizing dye is coupled with an addition polymerizable compoundstructure (for example, an acryloyl group and a methacryloyl group) by amethod including covalent bonding, ionic bonding, and hydrogen bonding,it is possible to strengthen the exposed film or to suppress unnecessarydeposition of the dye from the film after exposure. Furthermore, whenthe sensitizing dye is coupled with a radical, acid or base generatingpart of an activator compound as described layer, etc., it is possibleto markedly enhance the photosensitivity especially in a lowconcentration state of the initiation system. Moreover, for the purposeof enhancing the treatment aptitude against an (alkaline) aqueousdeveloping solution, an aspect of which is a preferred embodiment of thephoto-sensitive layer of the invention, it is effective to introduce ahydrophilic site (for example, acid groups or polar groups such as acarboxyl group and its esters, a sulfonic group and its esters, and anethylene oxide group). In particular, a hydrophilic group of an estertype has characteristic features that it is excellent in compatibilityin the photosensitive layer because it has a relatively hydrophobicstructure and that it generates an acid group due to hydrolysis in thedeveloping solution, thereby increasing the hydrophilicity. Besides, forexample, it is possible to properly introduce a substituent for thepurposes of enhancing the compatibility in the photosensitive layer andsuppressing the deposition of crystal. For example, in a certainphotosensitive system, there may be the case where an unsaturated bondsuch as an aryl group and an allyl group is very useful for enhancingthe compatibility. Furthermore, by introducing steric hindrance betweenthe π-planes of the dye by a method such as introduction of a branchedalkyl structure, it is possible to markedly suppress the deposition ofcrystal. Moreover, by introducing a phosphonic group, an epoxy group, atrialkoxysilyl group, etc., it is possible to enhance adhesion toinorganic materials such as metals and metal oxides. Besides, a methodfor polymerizing the sensitizing dye can be applied depending upon theintended purpose.

Details of the use method regarding which structure of the sensitizingdye is to be used, whether the sensitizing dye is to be used singly orin combination of two or more kinds thereof or what addition amount ofthe sensitizing dye is to be employed can be properly set up adaptivewith the performance design of an ultimate photographic material. Forexample, by jointly using two or more kinds of the sensitizing dyes, itis possible to enhance the compatibility with the photosensitive layer.In choosing the sensitizing dye, in addition to the photosensitivity, amolar absorption coefficient at a luminescence wavelength of a lightsource to be used is an important factor. By using a dye having a largemolar absorption coefficient, it is possible to make the addition amountof the dye relatively low. Therefore, use of such a dye is economicaland advantageous in view of film physical properties of thephotosensitive layer. Since the photosensitivity of the photosensitivelayer, the resolution, and the physical properties of the exposed filmare largely influenced by the absorbance at a wavelength of the lightsource, the addition amount of the sensitizing dye is to be properlychosen while taking into consideration these matters. For example, in aregion where the absorbance is low as 0.1 or less, the sensitivity islowered. Furthermore, the resolution becomes low due to the influence ofhalation. However, for the purpose of hardening a thick film of 5 μm ormore, there may be the case where when the absorbance is low in thisway, the hardness can be rather increased. Moreover, in a region wherethe absorbance is high as 3 or more, the major part of light is absorbedon the surface of the photosensitive layer, and hardening in the innerpart is hindered. For example, when used as a printing plate, the filmstrength and adhesion to a substrate become insufficient. In the use asa lithographic printing plate which is used in a relatively thin filmthickness, it is preferred to set up the addition amount of thesensitizing dye such that the absorbance of the photosensitive layer isin the range of from 0.1 to 1.5, and preferably from 0.25 to 1.Furthermore, in the application as a lithographic printing plate, theaddition amount of the sensitizing dye to be used is usually in therange of from 0.05 to 30 parts by weight, preferably from 0.1 to 20parts by weight, and more preferably from 0.2 to 10 parts by weightbased on 100 parts by weight of the photosensitive layer components.

(A2) Activator Compound:

The activator compound which is the second essential component of thephotoinitiation system in the composition of the invention will bedescribed below. The activator compound in the invention is a compoundwhich is to cause a chemical change through a mutual action with theelectron excited state of the sensitizing dye, thereby generating atleast one of a radical, an acid, and a base. The thus generated radical,acid or base will be hereinafter referred to simply as “active species”.In the case where such a compound is absent, or in the case where onlythe activator compound is used singly, practically satisfactorysensitivity is not obtained. However, as one embodiment of using theactivator compound jointly with the foregoing sensitizing dye, it isalso possible to apply them as a single compound by an adequate chemicalmethod (for example, connection by chemical bonding of the sensitizingdye to the activator compound). Such technical thoughts are disclosedin, for example, Japanese Patent No. 2,720,195.

In general, it is thought that the major part of these activatorcompounds generate an active species through an initial chemical processof any one of the following (1) to (3). That is, there are included (1)reductive decomposition of the activator compound on a basis of anelectron transfer reaction from the electron excited state of thesensitizing dye to the activator compound; (2) oxidative decompositionof the activator compound on a basis of electron transfer from theactivator compound to the electron excited state of the sensitizing dye;and (3) decomposition from the electron excited state of the activatorcompound on a basis of energy transfer from the electron excited stateof the sensitizing dye to the activator compound. Among the foregoing(1) to (3) types, what type the individual activator compound belongs tois often vague. However, an important characteristic feature of thesensitizing dye in the invention resides in the matter that a very highsensitizing effect can reveal through a combination with any type ofactivator compound.

As specific activator compounds, ones which are known by those skilledin the art can be used without limitations. Specifically, a number ofactivator compounds are described in, for example, Bruce M. Monroe, etal., Chemical Revue, 93, 435 (1993); R. S. Davidson, Journal ofPhotochemistry and Biology A: Chemistry, 73, 81 (1993); J. P. Faussier,“Photoinitiated Polymerization-Theory and Applications”. Rapra Review,Vol. 9, Report, Rapra Technology (1998); and T. Tsunooka, et al., Prog.Polym. Sic, 21, 1 (1996). Furthermore, as other compound groups havingthe foregoing functions (1) and (2), there are also known compoundgroups which oxidatively or reductively generate bond cleavage, asdescribed in, for example, F. D. Saeva, Topics in Current Chemistry,156, 59 (1990); G. G. Maslak, Topics in Current Chemistry, 168, 1(1993); H. B. Shuster, et al., JACS, 112, 6329 (1990); and I. D. F.Baton, et al., JACS, 102, 3298 (1980).

Specific examples of the preferred activator compound will be describedbelow while classifying into (a) one which is reduced to cause bondcleavage, thereby generating an active species, (b) one which isoxidized to cause bond cleavage, thereby generating an active species,and (c) others. However, with respect to what class the individualcompound belongs to, there is often no commonly accepted theory, and itshould be construed that the invention is never restricted by anydescription regarding these reaction mechanisms.

(a) One Which is Reduced to Cause Bond Cleavage, Thereby Generating anActive Species:

Compounds having a carbon-halogen bond: It is considered that thecarbon-halogen bond is reductively cleaved to generate an active species(as described in, for example, Polymer Preprints, Jpn., 41(3), 542(1992)). A radical or an acid can be generated as the active species.Specific examples of the compound which can be suitably used includehalomethyl-s-triazines; and besides, halomethyl oxadiazoles which can beeasily synthesized by those skilled in the art by a synthesis method asdescribed in M. P. Hutt, E. F. Elslager and L. M. Merbel, Journal ofHeterocyclic Chemistry, 7, 511 (1970); and compounds described in eachof German Patents Nos. 2,641,100, 3,333,450, 3,021,590 and 3,021,599.

Compounds having a nitrogen-nitrogen bond or a nitrogen-containinghetero ring-nitrogen-containing hetero ring bond: Bond cleavage isreductively caused (as described in, for example, J. Pys. Chem., 96, 207(1992)). Specifically, hexaaryl biimidazoles can be suitably used. Theactive species as generated is a lophine radical. When used jointly witha hydrogen-providing material as the need arises, it starts a radicalchain reaction, and besides, image formation using an oxidation reactionby a lophine radical is known (as described in J. Imaging Sci., 30, 215(1986)).

Compounds having an oxygen-oxygen bond: It is considered that theoxygen-oxygen bond is reductively cleaved to generate an active radical(as described in, for example, Polym. Adv. Technol., 1, 287 (1990)).Specifically, for example, organic peroxides are suitably used. Aradical can be generated as the active species.

Onium compounds: It is considered that a carbon-hetero bond or anoxygen-nitrogen bond is reductively cleaved to generate an activespecies (as described in, for example, J. Photopolym. Sci. Technol., 3,149 (1990)). Specific examples of the onium compound which can besuitably used include iodonium salts as described in European Patent No.104,143, U.S. Pat. No. 4,837,124, JP-A-2-150848, and JP-A-2-96514;sulfonium salts as described in European Patents Nos. 370,693, 233,567,297,443, 297,442, 279,210 and 422,570 and U.S. Pat. Nos. 3,902,144,4,933,377, 4,760,013, 4,734,444 and 2,833,827; diazonium salts (forexample, optionally substituted benzenediazonium); diazonium salt resins(for example, a formaldehyde resin of diazodiphenylamine);N-alkoxypyridinium salts (for example, ones described in U.S. Pat. No.4,743,528, JP-A-63-138345, JP-A-63-142345, JP-A-63-142346, andJP-B-46-42363, and specifically 1-methoxy-4-phenylpyridiniumtetrafluoroborate, etc.); and compounds as described in IP-B-52-147277,JP-B-52-14278, and JP-B-52-14279. A radical or an acid is generated asthe active species.

Active esters: Nitrobenzyl esters of a sulfonic acid or a carboxylicacid, esters of a sulfonic acid or a carboxylic acid and an N-hydroxycompound (for example, N-hydroxyphthalimide and oximes), sulfonic acidesters of pyrogallol, naphthoquinonediazide-4-sulfonic acid esters, andthe like can be reductively cleaved. A radical or an acid can begenerated as the active species. Specific examples of sulfonic acidesters include nitrobenzyl ester compounds as described in EuropeanPatents Nos. 0,290,750, 046,083, 156,153, 271,851 and 0,388,343, U.S.Pat. Nos. 3,901,710 and 4,181,531, JP-A-60-198538, and JP-A-53-133022;iminosulfonate compounds as described in European Patents Nos.0,199,672, 84,515, 199,672, 044,115 and 0,101,122, U.S. Pat. Nos.4,618,564, 4,371,605 and 4,431,774, JP-A-64-18143, JP-A-2-245756, andJP-A4-365048; and compounds as described in JP-B-62-6223, JP-B-63-14340,and JP-A-59-17483 1. Furthermore, there are enumerated the followingcompounds.

In the formulae, Ar represents an optionally substituted aromatic groupor aliphatic group.

It is also possible to generate a base as the active species, and forexample, the following compound groups are known

Ferrocene and iron-allene complexes. An active radical can bereductively generated. Specific examples are disclosed in JP-A-1-304453and JP-A-1-152109.

In the formulae, R represents an optionally substituted aliphatic groupor aromatic group.

Disulfones: An S—S bond cleavage can be reductively caused to generatean acid. For example, diphenyldisulfones as described in JP-A-61-166544are known.

(b) One which is oxidized to cause bond cleavage, thereby generating anactive species:

Alkylate complexes: It is considered that a carbon-hetero bond isoxidatively cleaved to generate an active radical (as described in, forexample, J. Am. Chem. Soc., 112, 6329 (1990)). Specifically, forexample, triarylalkyl borates are suitably used.

Alkylamine compounds: It is considered that a C—X bond on the carbonadjacent to nitrogen is cleaved due to oxidation to generate an activeradical (as described in, for example, J. Am. Chem. Soc., 116, 4211(1994)). X is suitably a hydrogen atom, a carboxyl group, atrimethylsilyl group, a benzyl group, etc. Specific examples of thealkylamine compound include ethanolamines, N-phenylglycines, andN-trimethylsilylmethylanilines.

Sulfur-containing and tin-containing compounds: Ones resulting fromsubstitution of the nitrogen atom of the foregoing amine with a sulfuratom or a tin atom can generate an active radical due to a similaraction. It is also known that a compound having an S—S bond causessensitization due to S—S cleavage.

α-Substituted methylcarbonyl compounds: An active radical can begenerated due to bond cleavage between carbonyl and α-carbon uponoxidation. Ones resulting from conversion of the carbonyl into oximeether exhibit a similar action. Specific examples of the compoundinclude 2-alkyl-1-[4-(alkylthio)phenyl]-2-morpholinopropanone-1compounds and oxime ethers obtained by reacting such a compound with ahydroxylamine and then etherifying the N—OH.

Sulfinic acid salts: An active radical can be reductively generated.Specific examples thereof include sodium arylsulfinates.

(c) Others:

While the sensitization mechanism is not elucidated yet, there are anumber of compounds capable of functioning as the activator compound.Specific examples thereof include organometallic compounds such astinanocenes, aromatic ketones, acyl phosphines, and bisacyl phosphines.A radical or an acid can be generated as the active species.

Among the activator compounds which are used in the invention, preferredcompound groups which are especially excellent in sensitivity andstability will be specifically enumerated below.

(1) Halomethyltriazines:

There is enumerated a compound represented by the following formula [I].This compound is especially excellent in the radical generating or acidgenerating ability

In the formula [I], X represents a halogen atom. Y¹ represents —CX′₃,—NH₂, —NHR^(1′), —N(R^(1′))₂, or —OR^(1′). Here, R^(1′) represents analkyl group, a substituted alkyl group, an aryl group, or a substitutedaryl group. R¹ represents —CX₃, an alkyl group, a substituted alkylgroup, an aryl group, a substituted aryl group, or a substituted alkenylgroup.

Specific examples of such a compound include compounds as described in,for example, Wakabayashi, et al., Bull. Chem. Soc. Japan, 42, 2924(1969), such as 2-phenyl-4,6-bis(trichloromethyl)-S-triazine,2-(p-chlorophenyl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-tolyl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)-S-triazine,2-(2′,4′-dichloro-phenyl)-4,6-bis(trichloromethyl)-S-triazine,2,4,6-tris(trichloromethyl)-S-triazine,2-methyl-4,6-bis(trichloromethyl)-S-triazine,2-n-nonyl-4,6-bis(trichloromethyl)-S-triazine, and2-(α,α,β-trichloroethyl)-4,6-bis(trichloromethyl)-S-triazine. Besides,there can be enumerated compounds as described in U.K. Patent No.1,388,492, such as 2-styryl-4,6-bis(trichloromethyl)-S-triazine,2-(p-methyl-styryl)-4,6-bis(trichloromethyl)-S-triazine,2-(p-methoxy-styryl)-4,6-bis(trichloromethyl)-S-triazine, and2-(p-methoxystyryl)-4-amino-6-trichloromethyl-S-triazine; compounds asdescribed in JP-A-53-133428, such as2-(4-methoxy-naphtho-1-yl)-4,6-bis-trichloromethyl-S-triazine,2-(4-ethoxy-naphtho-1-yl)-4,6-bis-trichloromethyl-S-triazine,2-[4-(2-ethoxyethyl)-naphtho-1-yl]-4,6-bis-trichloromethyl-S-triazine,2-4,7-di -methoxy-naphtho-1-yl)-4,6-bis-trichloromethyl-S-triazine, and2-(acenaphtho-5-yl)-4,6-bis-trichloromethyl-S-triazine; and compounds asdescribed in German Patent No. 3,337,024, such as the followingcompounds.

Furthermore, there can be enumerated compounds as described in F. C.Schaefer, et al., J. Org. Chem., 29, 1527 (1964), such as2-methyl-4,6-bis(tribromomethyl)-S-triazine,2,4,6-tris(tribromomethyl)-S-triazine,2,4,6-tris(dibromomethyl)-S-triazine,2-amino-4-methyl-6-tribromomethyl-S-triazine, and2-methoxy-4-methyl-6-trichloromethyl-S-triazine.

Moreover, there can be enumerated compounds as described inJP-A-62-58241, such as the following compounds.

Moreover, there can be enumerated compounds as described inJP-A-5-281728, such as the following compounds.

(2) Titanocenes:

As the titanocene compound which is especially suitably used as theactivator compound, any titanocene compound which when light exposed inthe copresence of the foregoing sensitizing dye, can generate an activespecies is useful. For example, known compounds as described inJP-A-59-152396, JP-A-61-151197, JP-A-63-41483, JP-A-63-41484,JP-A-2-249, JP-A-2-291, JP-A-3-27393, JP-A-3-12403, and JP-A-6-41170 canbe properly chosen and used.

More specifically, there can be enumerateddicyclopentadienyl-Ti-dihcloride, dicyclopentadienyl-Ti-bisphenyl,dicyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,6difluorophen-1-yl,dicyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,3,5,6tetrafluorophen-1-yl,dimethylcyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl, andbis(cyclopentadienyl)-bis(2,6-difluoro-3-(pyl-1-yl)phenyl)titanium.

(3) Borate Salt Compounds:

A borate salt represented by the following formula [II] is excellent inradical generating ability.

In the formula [II], R⁵¹, R⁵², R⁵³, and R⁵⁴ may be the same or differentand each represents a substituted or unsubstituted alkyl group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted alkynyl group, or asubstituted or unsubstituted heterocyclic group; and two or more groupsof R⁵¹, R⁵², R⁵³, and R⁵⁴ may be taken together to form a cyclicstructure, provided that at least one of R⁵¹, R⁵², R⁵³, and R⁵⁴ is asubstituted or unsubstituted alkyl group. Z⁺ represents an alkali metalcation or a quaternary ammonium cation.

The alkyl group represented by the foregoing R⁵¹ to R⁵⁴ includes linear,branched or cyclic alkyl groups and preferably has from 1 to 18 carbonatoms. Specific examples thereof include methyl, ethyl, propyl,isopropyl, butyl, pentyl, hexyl, octyl, stearyl, cyclobutyl,cyclopentyl, and cyclohexyl. Furthermore, the substituted alkyl groupincludes the foregoing alkyl groups which, however, have, as asubstituent, a halogen atom (for example, —Cl and —Br), a cyano group, anitro group, an aryl group (preferably a phenyl group), a hydroxylgroup, a group represented by the following formula:

(wherein R⁵⁵ and R⁵⁶ each independently represents a hydrogen atom, analkyl group having from 1 to 14 carbon atoms, or an aryl group), —COOR⁵⁷(wherein R⁵⁷ represents a hydrogen atom, an alkyl group having from 1 to14 carbon atoms, or an aryl group), or —COOR⁵⁸ or —OR⁵⁹ (wherein R⁵⁸ andR⁵⁹ each represents an alkyl group having from 1 to 14 carbon atoms oran aryl group).

The aryl group represented by the foregoing R⁵¹ to R⁵⁴ includesmonocyclic to tricyclic aryl groups such as a phenyl group and anaphthyl group; and the substituted aryl group includes the foregoingaryl groups which, however, have, as a substituent, any one of thesubstituents as in the foregoing substituted alkyl group or an alkylgroup having from 1 to 14 carbon atoms.

The alkenyl group represented by the foregoing R⁵¹ to R⁵⁴ includeslinear, branched or cyclic alkenyl groups having from 2 to 18 carbonatoms; and examples of the substituent of the substituted alkenyl groupinclude the same substituents as enumerated as the substituent of theforegoing substituted alkyl group.

The alkynyl group represented by the foregoing R⁵¹ to R⁵⁴ includeslinear or branched alkynyl groups having from 2 to 28 carbon atoms; andexamples of the substituent of the substituted alkynyl group include thesame substituents as enumerated as the substituent of the foregoingsubstituted alkyl group.

Furthermore, examples of the heterocyclic group represented by theforegoing R⁵¹ to R⁵⁴ include five or more membered rings containing atleast one of N, S and O. Of these, 5-membered to 7-membered heterocyclicgroups are preferable. The heterocyclic ring may contain a fused ring.The heterocyclic group may further have, as a substituent, the samesubstituent as enumerated as the substituent of the foregoingsubstituted aryl group.

Specific examples of the compound represented by the formula [II]include compounds as described in U.S. Pat. Nos. 3,567,453 and 4,343,891and European Patents Nos. 109,772 and 109,773 and the followingcompounds.

(4) Hexaaryl Biimidazoles:

Hexaaryl biimidazoles can generate a radical having excellent stabilityand high sensitivity, Specific examples thereof include2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetra-phenyl biimidazole,2,2′-bis(o-bromophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o,p-dichlorophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetra(m-methoxyphenyl) biimidazole,2,2′-bis-(o,o′-dichlorophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-nitrophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-methylphenyl)-4,4′,5,5′-tetraphenyl biimidazole, and2,2′-bis(o-trifluoromethylphenyl)-4,4′,5,5′-tetraphenyl biimidazole.

(5) Onium Salt Compounds:

Onium compounds of an element belonging to the group 15(5B), 16(6B) or17(7B) of the periodic table, specifically, N, P, As, Sb, Bi, O, S, Se,Te, or I are an activator having excellent sensitivity. In particular,iodonium salts and sulfonium salts, especially diaryl iodonium andtriaryl sulfonium salt compounds are extremely excellent from theviewpoints of both sensitivity and storage stability. These compoundscan generate an acid and/or a radical, and use conditions thereof can beproperly chosen and employed depending upon the intended purpose.Specific examples thereof include the following compounds.

(6) Organic Peroxides:

When an activator compound of an organic peroxide type is used, it ispossible to generate a radical as the active species with very highsensitivity.

The “organic peroxide” includes almost all of organic compounds havingat least one oxygen-oxygen bond in the molecule thereof. Examplesthereof include methyl ethyl ketone peroxide, cyclohexanone peroxide,3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide,acetylacetone peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis-(t-butylperoxy)butane,t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzenehydroperoxide, p-methane hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide, 1,1,3,3-tetramethylbutylhydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumylperoxide, bis(t-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, acetyl peroxide, isobutyrylperoxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide,3,5,5-trimethylhexanoyl peroxide, succinic acid peroxide, benzoylperoxide, 2,4-dichlorobenzoyl peroxide, m-toluoyl peroxide,diisopropylperoxy dicarbonate, di-2-ethylhexylperoxy dicarbonate,di-2-ethoxyethylperoxy dicarbonate, dimethoxyisopropylperoxy carbonate,di(3-methyl-3-methoxybutyl)peroxy dicarbonate, t-butylperoxy acetate,t-butylperoxy pivalate, t-butylperoxy neodecanoate, t-butyl-peroxyoctanoate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxy benzoate, di-t-butylperoxy isophthalate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl permaleate,t-butylperoxyisopropyl carbonate,3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone,3,3′,44′-tetra-(t-amylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-octylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(cumylperoxycarbonyl)benzopbenone,3,3′,4,4′-tetra(p-isopropylcumyl-peroxycarbonyl)benzophenone, carbonyldi(t-butylperoxy dihydrogen diphthalate), and carbonyl di(t-hexylperoxydihydrogen diphthalate).

Of these, peracid esters such as3,3′,4,4′-tetra(t-butyl-peroxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-amylperoxycabonyl)benzophenone,3,3′,4,4′-tetra(t-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-octylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(cumylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(p-isopropylcumylperoxycarbonyl)benzophenone, anddi-t-butylperoxy isophthalate are preferable.

Of these active compounds, (1) halomethyltriazines, (2) titanocenes, and(4) hexaaryl biimidazoles are especially preferable; and (2) titanocenecompounds are the most preferable.

Likewise the preceding sensitizing dye, with respect to the foregoingactivator compound, it is also possible to carry out a variety ofchemical modifications for the purpose of improving characteristics ofthe photosensitive layer. For example, there can be applied methods suchas coupling with the sensitizing dye, an addition polymerizableunsaturated compound and other activator part, introduction of ahydrophilic site, enhancement of compatibility, introduction of asubstituent for the purpose of suppressing the deposition of crystal,introduction of a substituent for the purpose of enhancing adhesion, andpolymerization.

Likewise the preceding sensitizing dye, with respect to the use methodof such an activator compound, it can be arbitrarily set up by properlydesigning the performance of the photographic material. For example, byusing two or more kinds of the activator compounds Jointly, it ispossible to enhance the compatibility with the photosensitive layer. Ingeneral, it is advantageous in view of the photosensitivity that theamount of the activator compound to be used is high. When the activatorcompound is used in an amount in the range of from 0.5 to 80 parts byweight, and preferably from 1 to 50 parts by weight based on 100 partsby weight of the photosensitive layer components, sufficientphotosensitivity is obtained. On the other hand, in the case where theactivator itself has absorption against visible light as in, forexample, titanocene compounds, in the use under a yellow or white lamp,it is preferable that the amount of the activator to be used is low inview of fogging properties due to light in the vicinity of 500 nm.However, by combining with the sensitizing dye of the invention, evenwhen the amount of the activator compound to be used is decreased to notmore than 6 parts by weight, further to not more than 1.9 parts byweight, and still further to not more than 1.4 parts by weight, it ispossible to obtain sufficient photosensitivity,

(B. Component (iii))

The third essential component (iii) in the composition of the inventionis a compound whose physical or chemical characteristics thereof changeirreversibly due to an action of the active species as generated byphotoreaction of the foregoing photoinitiation system. As the component(iii), arbitrary compounds having such properties can be used withoutparticular limitations. For example, in many cases, the compounds asenumerated in the foregoing initiation system have such propertiesthemselves. The characteristics of the component (iii) which change dueto any one of the radical or acid as generated from the photoinitiationsystem include, for example, changes in molecular physical properties(for example, absorption spectrum (color), chemical structure, andpolarizability) and material physical properties (for example,solubility, strength, refractive index, fluidity, and stickiness).

For example, when an acid or a base is generated from the initiationsystem by using, as the component (iii), a compound whose absorptionspectrum changes due to pH such as a pH indicator, it is possible tochange the hue only in the exposed area. Such a composition is useful asan image forming material. Similarly, in the case of using, as thecomponent (iii), a compound whose absorption spectrum changes due tooxidation and reduction or nucleic addition reaction, it is possible tocause oxidation, reduction, etc. due to a radical as generated from theinitiation system, thereby forming an image. Such examples are disclosedin, for example, J. Am. Chem. Soc., 108, 128 (1986), J. Imaging. Sci.,30, 215 (1986), and Israel. J. Chem., 25, 264 (1986).

Furthermore, by using, as the component (iii), a compound which can besubjected to addition polymerization or polycondensation and combiningit with the initiation system, it is possible to form a photocurableresin or a negative working photopolymer.

As the component (iii), there are used radical polymerizable compounds(for example, ethylenically unsaturated double bond-containingcompounds), cationic polymerizable compounds (for example, epoxycompounds, vinyl ether compounds, and methylol compounds), and anionicpolymerizable compounds (for example, epoxy compounds). Such examplesare described in, for example, Conference of Photopolymer Science andTechnology Ed., Photopolymer Handbook, published by Kogyo ChosakaiPublishing Inc. (1989) and Kobunshi, 45, 786 (1996). Furthermore,compositions comprising a combination of a thiol compound as thecomponent (iii) with a photo radical generation system are well known.

It is also useful to use an acid decomposable compound as the component(iii) and combine it with a photo acid generator. For example, materialsin which a polymer whose side chain or principal chain is decomposed byan acid is used, thereby changing solubility, hydrophilicity,hydrophobicity, etc. by light are put into practical use widely as aphoto decomposition type photosensitive resin or a positive workingphotopolymer. Specific examples thereof are described in, for example,ACS. Symp. Ser., 242, 11 (1984), JP-A-60-3625, U.S. Pat. Nos. 5,102,771,5,206,317 and 5,212,047, JP-A-4-26850, JP-A-3-192173, JP-A-60-10247, andJP-A-62-40450.

The ethylenically unsaturated double bond-containing additionpolymerizable compound which is the component (iii) which is especiallyexcellent for the purpose for obtaining a high-density lithographicprinting plate as one of the objects of the invention will be describedbelow in more detail

(B-1) Addition Polymerizable Compound:

The addition polymerizable compound having at least one ethylenicallyunsaturated double bond which is preferable as the component (iii) to beused in the invention is selected from compounds having at least one,and preferably two or more terminal ethylenically unsaturated doublebonds. Such compound groups are broadly known in the subject industrialfield and can be used in the invention without particular limitations.Such a compound has a chemical morphology such as monomers andprepolymers, namely dimers, trimers and oligomers, or mixtures thereofand copolymers thereof. Examples of monomers and copolymers thereofinclude unsaturated carboxylic acids (for example, acrylic acid,methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, andmaleic acid) and esters and amides thereof. Above all, esters between anunsaturated carboxylic acid and an aliphatic polyhydric alcohol andamides between an unsaturated carboxylic acid and an aliphaticpolyhydric amine compound are preferably used. Furthermore, additionreaction products between an unsaturated carboxylic acid ester or amidehaving a nucleic substituent (for example, a hydroxyl group, an aminogroup, and a mercapto group) and a monofunctional or polyfunctionalisocyanate or epoxy and dehydration condensation reaction productsbetween the foregoing unsaturated carboxylic acid ester or amide and amonofunctional or polyfunctional carboxylic acid are also suitably used.Further, addition reaction products between an unsaturated carboxylicacid ester or amide having an electrophilic substituent (for example, anisocyanate group and an epoxy group) and a monofunctional orpolyfunctional alcohol, amine or thiol and substitution reactionproducts between an unsaturated carboxylic acid ester or amide having aneliminating substituent (for example, a halogen group and a tosyloxygroup) and a monofunctional or polyfunctional alcohol, amine or thiolare also suitable. Furthermore, as another example, compound groupsresulting from substitution of the foregoing unsaturated carboxylic acidwith an unsaturated phosplionic acid, styrene, vinyl ether, etc. can beused.

With respect to specific examples of the monomer of the ester between analiphatic polyhydric alcohol compound and an unsaturated carboxylicacid, examples of acrylic esters include ethylene glycol diacrylate,triethylene glycol diacrylate, 1,3-butanediol diacrylate, tetramethyleneglycol diacrylate, propylene glycol diacrylate, neopentyl glycoldiacrylate, trimethylolpropane triacrylate, trimethylolpropanetri(acryloyloxypropyl) ether, trimethylolethane triacrylate, hexanedioldiacrylate, 1,4-cyclohexanediol diacrylate, tetraethylene glycoldiacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, dipentaerythritol diacrylate,dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitoltetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate,tri(acryloyloxyethyl) isocyanurate, and polyester acrylate oligomers.

Examples of methacrylic esters include tetramethylene glycoldimethacrylate, triethylene glycol dimethacrylate, neopentyl glycoldimethacrylate, trimethylolpropane trimethacrylate, trimethylolethanetrimethacrylate, ethylene glycol dimethacrylate, 1,3-butanedioldimethacrylate, hexanediol dimethacrylate, pentaerythritoldimethacrylate, pentaerythritol trimethacrylate, pentaerythritoltetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritolhexamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate,bis[p-(3-methacryloxy-2-hydroxypropoxy)pheny]dimethylmethane, andbis[p-(methacryloxyethoxy)pheny]dimethylmethane.

Examples of itaconic esters include ethylene glycol diitaconate,propylene glycol diitaconate, 1,3-butanediol diitaconate, 1,4-butanedioldiitaconate, tetraethylene glycol diitaconate, pentaerythritoldiitaconate, and sorbitol tetraitaconate.

Examples of crotonic esters include ethylene glycol dicrotonate,tetramethylene glycol dicrotonate, pentaerythritol dicrotonate, andsorbitol tetradicrotonate.

Examples of isocrotonic esters include ethylene glycol diisocrotonate,pentaerythritol diisocrotonate, and sorbitol tetraisocrotonate.

Examples of maleic esters include ethylene glycol dimaleate, triethyleneglycol dimaleate, pentaerythitol dimaleate, and sorbitol tetramaleate.

As examples of other esters, aliphatic alcohol based esters as describedin JP-B-46-27926, JP-B-51-47334, and JP-A-57-196231; esters having anaromatic based skeleton as described in JP-A-59-5240, JP-A-59-5241, andJP-A-2-226149: and amino group-containing esters as described inJP-A-1-165613 are also suitably used.

Furthermore, the foregoing ester monomers can be used as a mixture.

Furthermore, specific examples of the monomer of the amide between analiphatic polyhydric amine compound and an unsaturated carboxylic acidinclude methylene bis-acrylamide, methylene bis-methacrylamide,1,6-hexamethylene bis-acrylamide, 1,6-hexamethylene bis-methacrylamide,diethylenetriamine trisacrylamide, xylylene bisacrylamdie, and xylylenebismethacrylamide.

As other examples of the preferred amide-based monomer, ones having acyclohexylene structure as described in JP-B-54-21726 can be enumerated.

Furthermore, urethane based addition polymerizable compounds which areproduced by using an addition reaction between an isocyanate and ahydroxyl group are also suitable. Specific examples thereof includevinyl urethane compounds containing two or more polymerizable vinylgroups in one molecule, which are obtainable by adding a hydroxylgroup-containing vinyl monomer represented by the following formula(III) to a polyisocyanate compound containing two or more isocyanategroups in one molecule, as described in JP-B-48-41708.CH₂═C(R)COOCH₂CH(R′)OH  (III)

In the formula, R and R′ each independently represents H or CH₃.

Furthermore, urethane acrylates as described in JP-A-51-37193,JP-B-2-32293, and JP-B-2-16765; and urethane compounds having anethylene oxide based skeleton as described in JP-B-58-49860,JP-B-56-17654, JP-B-62-39417, and JP-B-62-39418 are also suitable.

Moreover, it is possible to obtain a photopolymerizable compositionhaving very excellent photosensitive speed by using an additionpolymerizable compound having an amino structure or a sulfide structurein the molecule thereof as described in JP-A-63-277653, JP-A-63-260909,and JP-A-1-105238.

As other examples, there can be enumerated polyester acrylates andpolyfunctional acrylates or methacrylates of an epoxy acrylateobtainable by reacting an epoxy resin with (meth)acrylic acid, asdescribed in JP-A-48-64183, JP-B-49-43191, and JP-B-52-30490. There canbe also enumerated specific unsaturated compounds as described inJP-B-46-43946, JP-B-1-40337, and JP-B-1-40336; and vinyl phosphonic acidbased compounds as described in JP-A-2-25493. In some case, there aresuitably used structures containing a perfluoroalkyl group as describedin JP-A-61-22048. Photocurable monomers and oligomers as introduced inJournal of the Adhesion Society of Japan, Vol. 20, No. 7, pages 300 to308 (1984) can also be used.

With respect to these addition polymerizable compounds, details of theuse method regarding what structure should be used, whether the additionpolymerizable compound should be used singly or jointly, and whataddition amount should be employed can be arbitrarily set up adaptivewith the design of the ultimate performance of the photographicmaterial. For example, the addition polymerizable compound is chosenfrom the following viewpoints. With respect to the photosensitive speed,a structure having a high content of an unsaturated group per moleculeis preferable, and in many cases, bifunctional or polyfunctionalcompounds are preferable. For the purpose of increasing the strength ofan image area, namely a cured film, trifunctional or polyfunctionalcompounds are preferable, Furthermore, a method for regulating both thephotosensitivity and the strength by jointly using compounds having adifferent functionality and a different polymerizable group (forexample, acrylic esters, methacrylic esters, styrene based compounds,and vinyl ether based compounds) is effective. There may be the casewhere while a compound having a high molecular weight or a compoundhaving high hydrophobicity is excellent in the photosensitive speed andfilm strength, it is not preferable in view of the development speed anddeposition in a developing solution. Furthermore, a method for choosingand using the addition polymerizable compound is an important factorwith respect to compatibility and dispersibility with other componentsin the photosensitive layer (for example, a binder polymer, aninitiator, and a coloring agent). For example, the compatibility ispossibly enhanced by using a low-purity compound or by jointly using twoor more kinds of compounds. Moreover, for the purpose of enhancingadhesion to a support, an overcoat layer, etc., a specific structure maybe selected. With respect to the blending ratio of the additionpolymerizable compound in the photosensitive layer, it is advantageousin view of the sensitivity that the blending ratio is high. However,when the blending ratio is too high, there are possibly caused problemssuch as occurrence of undesired phase separation, problems in theproduction step due to tackiness of the photosensitive layer (forexample, transfer of photographic material components and productionfailure derived from the tackiness), and deposition from the developingsolution. From these viewpoints, in many cases, the blending ratio ofthe addition polymerizable compound is from 5 to 80% by weight, andpreferably from 25 to 75% by weight based on the whole of components ofthe composition. These addition polymerizable compounds may be usedsingly or in admixture of two or more kinds thereof. Besides, withrespect to the use method of the addition polymerizable compound,adequate structure, blending and addition amount can be arbitrarilychosen from the viewpoints of a degree of polymerization hindranceagainst oxygen, a resolution, fogging properties, a change of refractiveindex, surface tackiness, etc. According to circumstances, a layerconstruction and a coating method such as undercoating and top coatingmay be employed.

(C. Binder Polymer)

In applying to a lithographic printing plate, an aspect of which is apreferred embodiment of the invention, it is preferred to further use abinder polymer in the photosensitive composition. It is preferred tocontain a linear organic polymer as the binder. As such “linear organicpolymer”, any polymer may be used. Preferably, linear organic polymerswhich enable one to achieve water development or weakly alkaline waterdevelopment and which are soluble or swellable in water or weaklyalkaline water are selected. The linear organic polymer is selected andused according to the applications not only as a film forming agent ofthe composition but also as water, weakly alkaline water or an organicsolvent developer. For example, by using a water-soluble organicpolymer, water development becomes possible. Examples of such a linearorganic polymer include addition polymers having a carboxyl group in theside chain thereof, for example, ones as described in JP-A-59-44615,JP-B-54-34327, JP-B-58-12577, JP-B-54-25957, JP-A-54-92723,JP-A-59-53836, and JP-A-59-71048, namely methacrylic acid copolymers,acrylic acid copolymers, itaconic acid copolymers, crotonic acidcopolymers, maleic acid copolymers, partially esterified maleic acidcopolymers, and the like. Similarly, acidic cellulose derivatives havinga carboxyl group in the side chain thereof can be enumerated. Besides,ones obtained by adding a cyclic acid anhydride to an addition polymerhaving a hydroxyl group are useful.

Of these, copolymers of [benzyl (meth)acrylate/(meth)acrylicacid/optionally other addition polymerizable vinyl monomer] andcopolymers of [allyl (meth)-acrylate/(meth)acrylic acid/optionally otheraddition polymerizable vinyl monomer] are especially suitable becausethey are excellent in balance among the film strength, the sensitivityand the developability.

Furthermore, acid group-containing urethane based binder polymers asdescribed in JP-B-7-120040, JP-B-7-120041, JP-B-7-120042, JP-B-8-12424,JP-A63-287944, JP-A63-287947, JP-A-1-271741, and JP-A-2003-270775 areadvantageous in view of printing resistance and low-exposure aptitudebecause they are very excellent in strength.

Moreover, amide group-containing binders as described in JP-A-11-171907are suitable because they have both excellent developability and filmstrength.

Additionally, polyvinylpyrrolidone, polyethylene oxide, and the like areuseful as the water-soluble linear organic polymer. Furthermore, for thepurpose of increasing the strength of the cured film) alcohol-solublenylons, polyethers between 2,2-bis-(4-hydroxyphenyl)-propane andepichlorohydrin, and the like are also useful. Such a linear organicpolymer can be mixed in an arbitrary amount in the entire composition.However, when the amount of the linear organic polymer exceeds 90% byweight, there are not given preferred results from the standpoints ofthe strength of an image to be formed and the like. The amount ispreferably from 30 to 85% by weight. Furthermore, it is preferable thata weight ratio of the photopolymerizable ethylenically unsaturateddouble bond-containing compound to the linear organic polymer is in therange of from 1/9 to 7/3. In a preferred embodiment, a binder polymerwhich is substantially insoluble in water and soluble in alkalis isused. In this way, it is possible to use a developing solution free froman organic solvent which is not preferred from the environmentalstandpoint, or to limit the amount of an organic solvent to a very smalllevel. In such a use method, an acid value of the binder polymer (thecontent of an acid per gram of the polymer as expressed in terms of thechemical equivalent number) and a molecular weight of the binder polymerare properly selected from the viewpoints of image strength anddevelopability. The acid value is preferably in the range of from 0.4 to3.0 meq/g; and the molecular weight is preferably in the range of from3,000 to 500,000. The acid value is more preferably in the range of from0.6 to 2.0 meq/g; and the molecular weight is more preferably in therange of from 10,000 to 300,000.

(D. Other Components)

In the photosensitive composition of the invention, other componentssuitable for the application, production process, and the like can befurther properly added. Preferred additives will be enumerated below.

(D1) Cosensitizer:

By using a certain kind of an additive (hereinafter referred to as“cosensitizer”), it is possible to further enhance the sensitivity.While these action mechanisms thereof are not always elucidated yet, itmay be considered that the majority thereof is based on the followingchemical process. That is, it is assumed that a variety of intermediateactive species (for example, radicals, peroxides, oxidizing agents, andreducing agents) as generated during the photoreaction which is starteddue to light absorption of the foregoing photoinitiation system and thesubsequently occurred addition polymerization reaction react with thecosensitizer to generate a new active radical. The cosensitizer isroughly classified into (a) a compound capable of generating an activeradical upon reduction, (b) a compound capable of generating an activeradical upon oxidation, and (c) a compound which is to react with aradical having low activity, whereby it is converted into a radicalhaving higher activity or acts as a chain transfer agent. However, inmany case, there is no commonly accepted theory on what class theindividual compound belongs to.

(a) Compound capable of Generating an Active Radical Upon Reduction:

Compounds having a carbon-halogen bond: It is considered that acarbonhalogen bond is reductively cleaved to generate an active radical.Specifically, for example, trihalomethyl-s-triazines and trihalomethyloxadiazoles can be suitably used.

Compounds having a nitrogen-nitrogen bond: It is considered that anitrogen-nitrogen bond is reductively cleaved to generate an activeradical. Specifically, for example, hexaaryl biimidazoles are suitablyused.

Compounds having an oxygen-oxygen bond: It is considered that anoxygen-oxygen bond is reductively cleaved to generate an active radical.Specifically, for example, organic peroxides are suitably used.

Onium compounds: It is considered that a nitrogen-hetero bond or anoxygen-nitrogen bond is reductively cleaved to generate an activeradical. Specifically, for example, diaryl iodonium salts, triarylsulfonium salts, and N-alkoxypyridium (azinium) salts are suitably used.

Ferrocene and iron-allene complexes: An active radical can bereductively generated.

(b) Compound Capable of Generating an Active Radical Upon Oxidation:

Alkylate complexes: It is considered that a carbon-hetero bond isoxidatively cleaved to generate an active radical. Specifically, forexample, triarylalkyl borates are suitably used.

Alkylamine compounds: It is considered that a C—X bond on the carbonadjacent to nitrogen is cleaved due to oxidation to generate an activeradical. X is suitably a hydrogen atom, a carboxyl group, atrimethylsilyl group, a benzyl group, etc. Specific examples of thealkylainine compound include ethanolamines, N-phenylglycines, andN-trimethylsilylmethylanilines.

Sulfur-containing and tin-containing compounds; Ones resulting fromsubstitution of the nitrogen atom of the foregoing amine with a sulfuratom or a tin atom can generate an active radical due to a similaraction. It is also known that a compound having an S—S bond causessensitization due to S—S cleavage.

α-Substituted methylcarbonyl compounds: An active radical can begenerated due to bond cleavage between carbonyl and α-carbon uponoxidation. Ones resulting from conversion of the carbonyl into oximeether exhibit a similar action. Specific examples of the compoundinclude 2-alkyl-1-[4-(alkylthio)phenyl]-2-morpholinopropanone-1compounds and oxime ethers obtained by reacting such a compound with ahydroxylamine and then etherifying the N—OH.

Sulfinic acid salts: An active radical can be reductively generated.Specific examples thereof include sodium arylsulfinates.

(c) Compound Which is to React with a Radical Having Low Activity,Whereby it is Converted into a Radical Having Higher Activity or Acts asa Chain Transfer Agent;

For example, compound groups having SH, PH, SiH, or GeH in the moleculethereof are used. These compounds can generate a radical by providing aradical species having low activity with hydrogen, or can generate aradical upon oxidation and then proton elimination Specifically, thereare enumerated 2-mercaptobenzimidazoles.

A number of more specific examples of the cosensitizer are described asadditives for the purpose of enhancing the sensitivity in, for example,JP-A-9-236913. A part of such specific examples will be given below, butit should not be construed that the invention is limited thereto.Incidentally, -TMS represents a trimethylsilyl group.

Likewise the preceding sensitizing dye, with respect to thecosensitizer, it is also possible to carry out various chemicalmodifications for the purpose of further improving characteristics ofthe photosensitive layer. For example, there can be applied methods suchas coupling with the sensitizing dye and the activator and an additionpolymerizable unsaturated compound and other part, introduction of ahydrophilic site, enhancement of compatibility, introduction of asubstituent for the purpose of suppressing the deposition of crystal,introduction of a substituent for the purpose of enhancing adhesion, andpolymerization.

The cosensitizer can be used singly or in combination of two or morekinds thereof. An amount of the cosensitizer to be used is in the rangeof from 0.05 to 100 parts by weight, preferably from 1 to 80 parts byweight, and more preferably from 3 to 50 parts based on 100 parts byweight of the ethylenically unsaturated double bond-containing compound.

(D2) Polymerization Inhibitor:

In the invention, in addition to the foregoing basic components, it isdesired to add a small amount of a thermal polymerization inhibitorduring the production or storage of the photosensitive composition forthe purpose of preventing unnecessary thermal polymerization of thepolymerizable ethylenically unsaturated double bond-containing compoundfrom occurring. Examples of a suitable thermal polymerization inhibitorinclude hydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol,t-butyl chatecol, benzoquinone, 4,4′-thiobis(3-methyl-6-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylpbenol), andN-nitrosophenylhydroxylamine cerous salt. An amount of the thermalpolymerization inhibitor to be added is preferably from about 0.01% byweight to about 5% by weight based on the weight of the entirecomposition. Furthermore, if desired, for the purpose of preventingpolymerization hindrance due to oxygen, a higher fatty acid derivativesuch as behenic acid and behenic amide may be added, thereby unevenlydistributing it on the surface of the photosensitive layer during adrying step to be carried out after coating. An amount of the higherfatty acid derivative to be added is preferably from about 0.5% byweight to about 10% by weight of the entire composition.

(D3) Coloring Agent:

For the purpose of coloring the photosensitive layer, a coloring agentsuch as dyes and pigments may be further added. In this way, it ispossible to enhance so-called plate inspection properties as a printingplate, such as visibility after plate making and aptitude to imagedensity analyzers. Specific examples of the coloring agent includepigments (for example, phthalocyanine based pigments, azo basedpigments, carbon black, and titanium oxide) and dyes (for example, EthylViolet, Crystal Violet, azo based dyes, anthraquinone based dyes, andcyanine based dyes). It is especially preferred to use a pigment as thecoloring agent. An amount of the coloring agent to be added ispreferably from about 0.5% by weight to about 5% by weight of the entirecomposition.

(D4) Other Additives:

In addition, known additives such as inorganic fillers for the purposeof improving physical properties of the cured film and besides, aplasticizer and a sensitizing agent capable of enhancing inkingproperties on the surface of the photosensitive layer may be added.

Examples of the plasticizer include dioctyl phthalate, didodecylphthalate, triethylene glycol dicaprylate, dimethyl glycol phthalate,tricresyl phosphate, dioctyl adipate, dibutyl sebacate, and triacetylglycerin When a binder is used, it can be added in an amount of not morethan 10% by weight based on the total weight of the ethylenicallyunsaturated double bond-containing compound and the binder.

Furthermore, in order to strength heating and exposure effects after thedevelopment for the purpose of enhancing the film strength (printingresistance), it is also possible to add UV initiators, thermalcrosslinking agents, and the like.

Besides, it is possible to add an additive or provide an interlayer forthe purpose of enhancing the adhesion of the photosensitive layer to thesupport or increasing development eliminating properties of an unexposedphotosensitive layer. For example, by adding or undercoating a compoundhaving a relatively strong mutual action with a substrate, such ascompounds having a diazonium structure and phosphonic compounds, it ispossible to enhance the adhesion or increase the printing resistance. Onthe other hand, by adding or undercoating a hydrophilic polymer such aspolyacrylic acid and polysulfonic acid, it is possible to enhancedevelopability of an non-image area or enhance staining resistance.

In coating the photopolymerizable composition of the invention on asupport, it is dissolved in a variety of organic solvents and thenprovided for use. Examples of the solvent which is used herein includeacetone, methyl ethyl ketone, cyclohexane; ethyl acetate, ethylenedichloride, tetrahydrofuran, toluene, ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol dimethyl ether,propylene glycol monomethyl ether, propylene glycol monoethyl ether,acetylacetone, cyclohexanone, diacetone alcohol, ethylene glycolmonomethyl ether acetate, ethylene glycol ethyl ether acetate, ethyleneglycol monoisopropyl ether, ethylene glycol monobutyl ether acetate,3-methoxypropanol, methoxyethoxyethanol, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycol dimethylether, diethylene glycol diethyl ether, propylene glycol monomethylether acetate, propylene glycol monoethyl ether acetate, 3-methoxypropylacetate, N,N-methylformamide, dimethyl sulfoxide, γ-butyrolactone,methyl lactate, and ethyl lactate. These solvents can be used singly orin admixture. A concentration of solids in the coating solution issuitably from 2 to 50% by weight.

The coating amount of the photosensitive layer on the support possiblyinfluences mainly sensitivity of the photosensitive layer,developability, and strength and printing resistance of the exposedfilm. It is desired that the coating amount is adequately chosendepending upon the application When the coating amount is too low, theprinting resistance becomes insufficient. On the other hand, when it istoo high, not only the sensitivity is lowered and it takes a long periodof time for the exposure, but also it takes a longer period of time forthe development treatment, and therefore, such is not preferable. For alithographic printing plate for scan exposure which is the major purposeof the invention, the coating amount is suitably in the range of fromabout 0.1 g/m² to about 10 g/m² in terms of the weight after drying. Thecoating amount is more preferably from 0.5 to 5 g/m².

(E. Support)

In order to obtain a lithographic printing plate containing thephotosensitive composition of the invention, it is desired to providethe foregoing photosensitive layer on a support, the surface of which ishydrophilic. As the hydrophilic support, conventionally knownhydrophilic supports which are useful in lithographic printing platescan be used without limitations. It is preferable that the support to beused is a dimensionally stable plate-like material. Examples of thesupport include papers, papers laminated with a plastic (for example,polyethylene, polypropylene, and polystyrene), metal plates (forexample, aluminum, zinc, and copper), plastic films (for example,cellulose diacetate, cellulose triacetate, cellulose propionate,cellulose butyrate, cellulose acetate butyrate, cellulose nitrate,polyethylene terephthalate, polyethylene, polystyrene, polypropylene,polycarbonates, and polyvinyl acetal), and papers or plastic filmshaving the foregoing metal laminated or vapor deposited thereon. Ifdesired, the surface of such a support may be subjected to a properknown physical or chemical treatment for the purposes of impartinghydrophilicity, enhancing the strength, and so on.

In particular, as the preferred support, there are enumerated papers,polyester films, and aluminum plates. Of these, aluminum plates whichhave good dimensional stability, are relatively cheap and can provide asurface having excellent hydrophilicity and strength by a surfacetreatment as the need arises are especially preferable. Furthermore, acomposite sheet having an aluminum sheet coupled on a polyethyleneterephthalate film as described in JP-B-48-18327 is also preferable.

Examples of the preferred aluminum plate include pure aluminum platesand alloy plates containing aluminum as the major component and a slightamount of foreign elements. Plastic films having aluminum laminated orvapor deposited thereon are also employable. Examples of foreignelements which are contained in aluminum alloys include silicon, iron,manganese, copper, magnesium, chromium, zinc, bismuth, nickel, andtitanium. The content of foreign elements in the alloy is at most 10% byweight. While the aluminum which is especially suitable in the inventionis pure aluminum, since it is difficult to produce completely purealuminum according to the smelting technology, a slight amount offoreign elements may be contained. With respect to the aluminum platewhich is applied in the invention in this way, its composition is notspecified, and aluminum plates made of a raw material which has hithertobeen publicly known and used can be properly utilized. The aluminumplate which is used in the invention is from about 0.1 mm to 0.6 mm,preferably from 0.15 mm to 0.4 mm, and especially preferably from 0.2 mmto 0.3 mm.

Moreover, in the case of a support having a surface of a metal,particularly aluminum, it is preferable that the support is subjected toa surface treatment such as a roughing (sand blasting) treatment, adipping treatment in an aqueous solution of sodium silicate, potassiumfluorozirconate, a phosphate, etc., and an anodic oxidation treatment.

The roughing treatment of the surface of the aluminum plate is carriedout by a variety of methods. For example, the roughing treatment iscarried out by a method for mechanically roughing the surface, a methodfor electrochemically dissolving and roughing the surface, or a methodfor selectively chemically dissolving the surface. As the mechanicalmethod, there can be employed known methods such as a ball polishingmethod, a brush polishing method, a blast polishing method, and a buffpolishing method. As the electrochemical roughing method, there isenumerated a method in which roughing is carried out in an electrolyicsolution of hydrochloric acid, nitric acid, etc. by an alternatingcurrent or a direct current. A combination of both of these methods asdisclosed in JP-A-54-63902 can also be utilized. Prior to roughing thealuminum plate, if desired, in order to remove a rolling oil on thesurface, for example, a degreasing treatment with a surfactant, anorganic solvent, an alkaline aqueous solution, etc. is carried out.

Moreover, an aluminum plate which after roughing, has been subjected toa dip treatment with a sodium silicate aqueous solution can bepreferably used. An aluminum plate which after performing an anodicoxidation treatment, has been subjected to a dip treatment with anaqueous solution of an alkali metal silicate as described inJP-B-47-5125 is suitably used. The anodic oxidation treatment is carriedout by, for example, passing an electric current in an electrolyticsolution composed of an aqueous solution or non-aqueous solution of aninorganic acid (for example, phosphoric acid, chromic acid, sulfuricacid, and boric acid) or an organic acid (for example, oxalic acid andsulfamic acid) or a salt thereof singly or in combination of two or morekinds thereof while using an aluminum plate as an anode.

Silicate electrodeposition as described in U.S. Pat. No. 3,658,662 isalso effective.

Moreover, a surface treatment combining a support which has beensubjected to electrograining with the foregoing anodic oxidationtreatment and sodium silicate treatment as described in JP-B-46-27481,JP-A-52-58602, and JP-A-52-30503 is useful.

Furthermore, a surface treatment for successively carrying outmechanical roughing, chemical etching, electrograining, anodic oxidationtreatment, and sodium silicate treatment as disclosed in JP-A-56-28893is suitable.

Moreover, after carrying out the foregoing treatments, a treatment forundercoating a water-soluble resin (for example, polyvinyl sulfonicacid, polymers or copolymers having a sulfonic group in the side chainthereof and polyacrylic acid), a water-soluble metal salt (for example,zinc borate), a yellow dye, an amine salt, etc. is suitable.

Moreover, a sol-gel treated substrate which has been subjected tocovalent bonding with a functional group capable of causing an additionreaction by a radical as disclosed in JP-A-7-154983 is suitably used.

As other preferred examples, there can be enumerated ones in which awaterproof hydrophilic layer is provided as a surface layer on anarbitrary support. Examples of such a surface layer include layerscomprising an inorganic pigment and a binder as described in U.S. Pat.No. 3,055,295 and JP-A-56-13168, hydrophilic swellable layers asdescribed in JP-A-9-80744, and sol-gel films comprising titanium oxide,polyvinyl alcohol, and a silicic acid as described in JP-T-8-507727.

Such a hydrophilic treatment is carried out for the purposes of makingthe surface of the support hydrophilic and besides, preventing a harmfulreaction of the photopolymerizable composition to be provided thereonand enhancing adhesion of the photosensitive layer.

(F. Protective Layer)

In a lithographic printing plate for scan exposure, an aspect of whichis a desired embodiment of the invention, since the exposure is usuallycarried out in the air, it is preferred to further provide a protectivelayer on the layer made of the photopolymerizable composition. Theprotective layer prevents mingling of low molecular compounds (forexample, oxygen and basic substances) present in the air, which likelyhinder the image forming reaction as generated by exposure in thephotosensitive layer, into the photosensitive layer from occurring,thereby making it possible to achieve exposure in the air. Accordingly,the protective layer is desired to have such characteristics that it haslow permeability of low molecular compounds such as oxygen; that it doesnot substantially hinder transmission of light to be used for exposure;that it has excellent adhesion to the photosensitive layer; and that itcan be easily removed in a development step after exposure. Devicesregarding such a protective layer have hitherto been made, and detailsthereof are described in U.S. Pat. No. 3,458,311 and JP-A-55-49729. Asmaterials which can be used in the protective layer, for example,water-soluble polymers having relatively excellent crystallinity can beused. Specifically, there are known water-soluble polymers such aspolyvinyl alcohol, polyvinylpyrrolidone, acidic celluloses, gelatin, gumarabic, and polyacrylic acid, Above all, what polyvinyl alcohol is usedas the major component brings the most satisfactory results in view ofbasic characteristics such as oxygen-blocking properties and developmenteliminating properties.

With respect to the polyvinyl alcohol which is used in the protectivelayer, so far as an unsubstituted vinyl alcohol unit for havingnecessary oxygen-blocking properties and water solubility is contained,a part thereof may be substituted with an ester, an ether or an acetal.Similarly, a part of the polyvinyl alcohol may have othercopolymerization component. As specific examples, there can beenumerated polyvinyl alcohols which are hydrolyzed to an extent of from71 to 100% by mole and which have a molecular weight in the range offrom 300 to 2,400. Specific examples thereof include PVA-105, PVA-110,PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HC,PVA-203, PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224,PVA-217EE, PVA-217E, PVA-220E, PVA-224E, PVA-405, PVA-420, PVA-613, andL-8, all of which are manufactured by Kuraray Co., Ltd.

Components (selection of PVA and use of an additive) and coating amountof the protective layer and the like are chosen while taking intoconsideration oxygen-blocking properties and development eliminatingproperties and besides, fogging properties, adhesion and scratchresistance. In general, the higher the degree of hydrolysis of PVA to beused (the higher the content of the unsubstituted vinyl alcohol unit inthe protective layer) or the thicker the film thickness, the higher theoxygen-blocking properties, and such is advantageous in view of thesensitivity However, when the oxygen-blocking properties are extremelyincreased, an unnecessary polymerization reaction likely occurs at thetime of production and at the time of unprocessed stock storage. Also,there is caused a problem that unnecessary fog or thickening of imagelines is caused at the time of image exposure. Also, adhesion to animage area and scratch resistance are extremely important in handling aplate. That is, when a hydrophilic layer made of a water-soluble polymeris laminated on a lipophilic polymer layer, film separation likelyoccurs due to a shortage of adhesive strength, and the separated portioncauses defects such as inferior film hardening due to polymerizationhindrance by oxygen. In contrast, there have been made various proposalsfor the purpose of improving adhesion between these two layers. Forexample, by mixing an acrylic emulsion, a water-insolublepolyvinylpyrrolidone-vinyl acetate copolymer, etc. in an amount of from20 to 60% by weight in a hydrophilic polymer composed mainly ofpolyvinyl alcohol and laminating the mixture on the polymer layer,sufficient adhesion is obtained. For the protective layer in theinvention, any of these known technologies ran be applied. The coatingmethod of such a protective layer is described in detail in, forexample, U.S. Pat. No. 3,458,311 and JP-A-55-49729.

Moreover, it is possible to impart. other function to the protectivelayer. For example, by adding a coloring agent to be used for exposure(for example, water-soluble dyes), which is excellent in transmissionagainst light of from 350 nm to 450 am and which can efficiently absorblight of 500 nm or more, it is possible to further increase safelightaptitude without causing a reduction of the sensitivity.

(G. Image Forming Method and Plate Making Process)

In using a photosensitive material using the photosensitive compositionof the invention as an image forming material, in general, after imageexposure, an unexposed area of the photosensitive layer is removed by adeveloping solution to obtain an image. In using such aphotopolymerizable composition in a lithographic printing plate,examples of the preferred developing solution include developingsolutions as described in JP-B-57-7427. Suitable examples thereofinclude aqueous solutions of an inorganic alkaline agent (for example,sodium silicate, potassium silicate, sodium hydroxide, potassiumhydroxide, lithium hydroxide, sodium triphosphate, sodium diphosphate,ammonium triphosphate, ammonium diphosphate, sodium metasilicate, sodiumbicarbonate, and ammonia water) and aqueous solutions of an organicalkaline agent (for example, monoethanolamine and diethanolamine). Suchan alkaline solution is added in a concentration of from 0.1 to 10% byweight, and preferably from 0.5 to 5% by weight.

Furthermore, such an alkaline aqueous solution can contain a smallamount of a surfactant or an organic solvent (for example, benzylalcohol, 2-phenoxyethanol, and 2-butoxyethanol) as the need arises. Forexample, there can be enumerated ones as described in U.S. Pat. Nos.3,375,171 and 3,615,480.

Moreover, developing solutions as described in JP-A-56-26601,JP-A-58-54341, JP-B-56-39464, and JP-B-56-42860 are also excellent.

As the especially preferred developing solution, there is enumerated adeveloping solution containing a nonionic compound represented by thefollowing formula (IV) and having a pH of from 11.5 to 12.8 and aconductivity of from 3 to 30 mS/cm as described in JP-A-2002-202616.A-W  (IV)

In the formula, A represents a hydrophobic organic group having a log Pof A-H of 1.5 or more; and W represents a nonionic hydrophilic organicgroup having a log P of W-H of less than 1.0.

Incidentally, the components of this developing solution are describedin detail in paragraphs (0024) to (0067) of JP-A-2002-202616.

In the invention, it is effective to add the nonionic compoundrepresented by the foregoing formula (IV) preferably in an amount offrom 0.1 to 15% by weight, and more preferably from 1.0 to 8.0% byweight in the developing solution.

Besides as a plate making process of a lithographic printing plateprecursor of the invention, the entire surface may be heated beforeexposure, during exposure or in the course of from exposure todevelopment as the need arises. By such heating, the image formingreaction in the photosensitive layer is promoted, thereby giving rise toadvantages such as enhancement of the sensitivity and printingresistance and stabilization of the sensitivity. Moreover, for thepurpose of enhancing the image strength and printing resistance, it isalso effective to carry out entire post-beating or entire exposure of animage after the development. Usually, it is preferable that the heatingbefore the development is carried out under a mild condition at nothigher than 150° C. Furthermore, for the heating after the development,a very strong condition is applied. Usually, the heating after thedevelopment is carried out at a temperature in the range of from 200 to500° C. When the temperature is 200° C. or higher, a sufficient imagestrengthening action is obtained, and when it is not higher than 500°C., problems such as deterioration of the support and thermaldecomposition of an image area do not occur.

With respect to the exposure method of a lithographic printing plate forscan exposure according to the invention, known methods can be employedwithout limitations. A desired wavelength of the light source is from350 nm to 450 nm, and specifically, an InGaN based semiconductor laseris suitable. With respect to the exposure mechanism, any of an internaldrum system, an external drum system, a flat bed system, and so on maybe employed. Furthermore, when a highly water-soluble material is usedas the photosensitive layer component of the invention, it is possibleto make the material soluble in neutral water or weakly alkaline water.There is also employable a system in which after mounting a lithographicprinting plate having such a construction on a printing machine,exposure and development are carried out on the machine.

As available laser light sources of from 350 nm to 450 nm, the followingcan be employed.

Examples of gas lasers include an Ar ion laser (364 nm, 351 nm, 10 mW to1W), a Kr ion laser (356 nm, 351 nm, 10 mW to 1 W), and an He—Cd laser(441 nm, 325 nm, 1 mW to 100 mW); and examples of solid lasers include acombination of {Nd:YAG(YVO₄) and SHG crystal} ×2 (355 nm, 5 mW to 1 W)and a combination of Cr:LiSAF and SHG crystal (430 nm, 10 mW); examplesof semiconductor laser systems include a KbO₃ ring resonator (430 nm, 30mW), a combination of a waveguide type wavelength converting element andAlGaAs and InGaAs semiconductors (380 nm to 450 nm, 5 mW to 100 mW), acombination of a waveguide type wavelength converting element andAlGaInP and AlGas semiconductors (300 nm to 350 nm, 5 mW to 100 mW), andAlGaInN (350 nm to 450 nm 5 mW to 30 mW); and besides, examples of pulselasers include an N₂ laser (337 nm, pulse: 0.1 to 10 mJ) and XeF (351nm, pulse: 10 to 250 mJ).

Of these, an AlGaInN semiconductor laser (commercially available InGaNbased semiconductor laser: 400 to 410 nm, 5 to 30 mW) is suitable inview of wavelength characteristics and costs.

Furthermore, as an exposure device of lithographic printing plate of thescan exposure system, examples of the exposure mechanism include aninternal drum system, an external drum system, and a flat bed system. Asa light source, all of the foregoing light sources exclusive of thepulse lasers can be utilized. Actually, the following exposure devicesare especially preferable with respect to the relationship between thesensitivity of the photographic material and the plate making time.

-   -   An exposure device of single beam using one gas laser or solid        laser light source according to the internal drum system.    -   An exposure device of single beam using a plural number (two or        more) of gas laser or a solid laser light sources according to        the internal drum system.    -   An exposure device of multi-beams using a plural number (ten or        more) of semiconductor lasers according to the flat bed system.    -   An exposure device of multi-beams using a plural number (ten or        more) of semiconductor lasers according to the external drum        system.

In the foregoing laser direct drawing type lithographic printing plates,in general, the following equation (eq 1) is valid among the sensitivityX of photographic material (J/cm²), the exposed area S of photographicmaterial (cm²), the power g per one laser light source (W), the number nof lasers, and the entire exposure time t (s).X·S=n·q·t  (eq 1)i) Case of an Internal Drum (Single Beam) System;

In general, the following equation (eq 2) is valid among the revolutionnumber f of laser (radian/s), the sub-scanning length Lx of photographicmaterial (cm), the resolution Z (dots/cm), and the entire exposure timet (s).f·Z·t=Lx  (eq 2)ii) Case of an External Drum (Multi-Beam) System:

In general, the following equation (eq 3) is valid among the revolutionnumber F of drum (radian/s), the sub-scanning length Lx of photographicmaterial (cm), the resolution Z (dots/cm), the entire exposure time t(s), and the number n of beams.F·Z·n·t=Lx  (eq 3)iii) Case of a Flat Bead (Multi-Beam) System:

In general, the following equation (eq 4) is valid among the revolutionnumber H of polygon mirror (radian/s), the sub-scanning length Lx ofphotographic material (cm), the resolution Z (dots/cm), the entireexposure time t (s), and the number n of beams.H·Z·n·t=Lx  (eq 4)

By substituting the exposure conditions of a resolution as required inan actual printing plate (2,560 dpi), a plate size (Al/Bl, sub-scanninglength: 42 inches) and about 20 sheets per hour and the photosensitivecharacteristics of the photosensitive composition of the invention(photosensitive wavelength and sensitivity: about 0.1 mJ/cm²) in theforegoing respective equations, it can be understood that in thephotographic material of the invention, a combination with themulti-beam exposure system of semiconductor laser is more preferable.Moreover, by further taking into consideration the operability, costs,etc., it is noted that a combination with a semiconductor lasermulti-beam exposure device of an external drum system is the mostpreferable.

Furthermore, as other exposure light sources for the photopolymerizablecomposition according to the invention, there can be employed respectivemercury vapor lamps (for example, an extra-high pressure mercury vaporlamp, a high pressure mercury vapor lamp, a medium pressure mercuryvapor lamp, and a low pressure mercury vapor lamp), chemical lamps,carbon arc lamps, xenon lamps, metal halide lamps, various laser lamps(for example, visible laser lamps and ultraviolet laser lamps),fluorescent lamps, tungsten lamps, and sunlight. Furthermore, withrespect to the utility of the photosensitive composition of theinvention, besides the utility as a lithographic printing plate for scanexposure, the photosensitive composition of the invention can be widelyapplied to ones known as utilities of photocurable resins withoutlimitations. For example, by applying to a photopolymerizablecomposition in a liquid state which is optionally used jointly with acationic polymerizable compound, a photofabrication material with highsensitivity is obtained. Furthermore, by utilizing a change of therefractive index which is caused following photopolymerization, ahologram material can be obtained. By utilizing a change of tackiness ofthe surface which is caused following photopolymerization, thephotosensitive composition of the invention can be applied to a varietyof transfer materials (for example, peel-apart photographic materialsand toner-developing photographic materials). The photosensitivecomposition of the invention can also be applied to photocuring ofmicrocapsules. The photosensitive composition of the invention can befurther applied for the production of electronic materials such asphotoresists and as inks and paints, and photocurable resin materialssuch as adhesives.

EXAMPLES

The invention will be described below with reference to the followingExamples, but it should not be construed that the invention is limitedto these Examples,

Synthesis Example 1 Synthesis of D1

2.7 g of phenylcarbazole carboxaldehyde, 0.35 g of pyrrolidine, and 1.34g of 3-coumaranone were dissolved in 50 mL of methanol, and the solutionwas then stirred for 2 hours while refluxing. After completion of thereaction, the reaction mixture was allowed to stand for cooling to roomtemperature, thereby depositing a yellow crystal. The deposited crystalwas filtered and added to 100 mL of methanol, and the mixture wasstirred for one hour. The resulting crystal was filtered and dried toobtain 3.3 g of the foregoing compound (D1) (yield: 85%, purity: 99.0%).

Identification was carried out by ¹H-NMR (CDCl₃), infrared absorptionspectrum, mass analytical spectrum, and elemental analysis. Electronabsorption spectrum (THF): absorption maximum wavelength, 422 nm,absorption maximum molar absorption coefficient, 38,800, oxidationpotential (CH₃CN, vs Ag/AgCl), +1.23 V.

Examples 1 to 16 and Comparative Examples 1 to 3

(Preparation of Support)

An aluminum plate having a thickness of 0.3 mm was dipped in and etchedwith 10% by weight sodium hydroxide at 60° C. for 25 seconds, washedwith running water, neutralized and washed with 20% by weight nitricacid, and then washed with water. The aluminum plate was subjected to anelectrolytic roughing treatment in a quantity of electricity at the timeof anode of 300 coulombs/dm² in a 1% by weight nitric acid aqueoussolution using an alternating waveform current of sine wave.Subsequently, the resulting aluminum plate was dipped in a 1% by weightsodium hydroxide aqueous solution at 40° C. for 5 seconds and thendipped in a 30% by weight sulfuric acid aqueous solution, subjected todesmutting at 60° C. for 40 seconds, and then subjected to an anodicoxidation treatment in a 20% by weight sulfuric acid aqueous solution ata current density of 2 A/dm² for 2 minutes such that an anodicallyoxidized film had a thickness of 2.7 g/m². A surface roughness thereofwas measured and found to be 0.3 μm (in terms of an Ra expressionaccording to JIS B0601).

The following sol-gel reaction solution was coated on the back surfaceof the thus treated substrate by using a bar coater and dried at 100° C.for one minute, thereby preparing a support provided with a backcoatlayer having a coating amount after drying of 70 mg/m².

Sol-Gel Reaction Solution:

Tetraethyl silicate: 50 parts by weight Water: 20 parts by weightMethanol: 15 parts by weight Phosphoric acid: 0.05 parts by weight  

The foregoing components were mixed and stirred. About 5 minutes later,heat generation started. After reacting for 60 minutes, the followingsolution was added to prepare a backcoat coating solution

Pyrogallol-formaldehyde condensation resin  4 parts by weight (molecularweight: 2,000): Dimethyl phthalate:  5 parts by weight Fluorine basedsurfactant (N-butyl  0.7 parts by weight perfluorooctanesulfonamideethyl acrylate/polyoxyethylene acrylate copolymer, molecular weight:20,000): Methanol silica gel (manufactured by Nissan  50 parts by weightChemical Industries, Ltd., 30% by weight in methanol): Methanol: 800parts by weight(Preparation of Photosensitive Layer)

A photopolymerizable composition having the following composition wascoated on the thus treated aluminum plate such that a coating amountafter drying was 1.0 g/m² to 2.0 g/m² and then dried at 80° C. for 2minutes, thereby forming a photosensitive layer.

Pentaerythritol tetraacrylate: 1.7 g Allyl methacrylate/methacrylicacid/N-isopropyl 1.9 g acrylamide copolymer (copolymerization molarratio: 70/15/15): Photopolymerization initiation system (as described inTable 1): Sensitizing dye (the foregoing Illustrative X g Compounds D1,3, 7, 10, 15, 16, 18, 25, 26, 28, 30, DR-1): Activator compound (thefollowing A-1 to A-6): Y g Cosensitizer (the following C-1 to C-3): Z gFluorine based nonionic surfactant (MEGAFAC 0.03 g F-780f, manufacturedby Dainippon Ink and Chemicals, Incorporated): Thermal polymerizationinhibitor 0.01 g (N-nitrosophenylhydroxylamine aluminum salt): Pigmentdispersion: 2.0 g Composition of pigment dispersion: Composition:Pigment Blue 15:6: 15 parts by weight Allyl methacrylate/methacrylicacid copolymer 10 parts by weight (copolymerization molar ratio: 83/17):Cyclohexanone: 15 parts by weight Methoxypropyl acetate: 20 parts byweight Propylene glycol monomethyl ether: 40 parts by weight Methylethyl ketone: 20 g Propylene glycol monomethyl ether: 20 g(Preparation of Protective Layer)

A 3% by weight aqueous solution of polyvinyl alcohol (degree ofhydrolysis: 98% by mole, degree of polymerization; 550) was coated onthis photosensitive layer such that a coating weight after drying was 2g/m² and then dried at 100° C. for 2 minutes.

(Evaluation of Photosensitivty)

FUJI STEP GUIDE (manufactured by Fuji Photo Film Co., Ltd., a gray scalein which a transmitted optical density discontinuously changes at a ΔDof 0.15) was brought into intimate contact with the thus obtainedphotographic material, which was then exposed by a xenon lamp through anoptical filter so as to have known exposure energy. Thereafter, theexposed photographic material was dipped in and developed with adeveloping solution having the following composition at 25° C. for 10seconds. The maximum step number at which an image was completelyremoved was read, and the exposure energy amount was determinedtherefrom, thereby calculating sensitivity (unit: mJ/cm²). The lowerthis value, the higher the sensitivity is. For the purpose of estimatingthe exposure aptitude with short wavelength semiconductor laser, KENKOBP-40 was used as the optical filter, and the exposure with monochromiclight of 400 nm was carried out. The results are shown in Table 1.

(Composition of Developing Solution)

Aqueous solution comprising the following composition and having a pH pf12.0:

Potassium hydroxide:  0.2 g 1K potassium silicate (SiO₂/K₂O = 1.9):  2.4g Compound represented by the following formula 1:  5.0 g Tetrasodiumethylenediaminetetraacetate:  0.1 g Water: 91.3 g

TABLE 1 Photoinitiation system Sensitizing dye Activator compoundCosensitizer Coating amount Clear sensitivity (X g) (Y g) (Z g) (mg/m²)(mJ/cm²) Example 1 D1 (0.20)  A-1 (0.35) C-2 (1.50) 1.40 0.25 Example 2D1 (0.20)  A-2-(0.20) C-2 (1.60) 1.10 0.15 Example 3 D1 (0.15)  A-3(0.30) Nil 1.10 0.30 Example 4 D1 (0.20)  A-4 (0.25) C-3 (1.50) 1.400.30 Example 5 D1 (0.15)  A-5 (0.30) C-1 (1.55) 1.10 0.25 Example 6 D1(0.15)  A-6 (0.35) Nil 1.40 0.35 Example 7 D15 (0.20) A-2 (0.15) C-2(1.50) 1.10 0.20 Example 8 D7 (0.10)  A-2 (0.10) Nil 1.30 0.25 Example 9D10 (0.15) A-1 (0.25) C-2 (1.50) 1.40 0.25 Example 10 D18 (0.10) A-1(0.30) Nil 1.10 0.25 Example 11 D3 (0.25)  A-3 (0.35) Nil 1.40 0.30Example 12 D26 (0.20) A-2 (0.20) C-2 (1.50) 1.30 0.20 Example 13 D25(0.20) A-2 (0.15) Nil 1.30 0.20 Example 14 D28 (0.20) A-2 (0.15) C-2(1.50) 1.40 0.15 Example 15 D16 (0.20) A-1 (0.35) C-2 (1.50) 1.10 0.20Example 16 D30 (0.20) A-3 (0.30) Nil 1.40 0.35 Comparative Nil A-1(0.35) C-2 (1.50) 1.40 No image was Example 1 formed. Comparative D1(0.20)  Nil C-2 (1.50) 1.40 No image was Example 2 formed. ComparativeDR-1 A-1 (0.35) C-2 (1.50) 1.40 1.60 Example 3

It is clear from Table 1 that Examples 1 to 16 using the initiationsystem of the invention exhibit sufficiently high sensitivity forpractical use. In comparison with Comparative Examples 1 to 3 not usingthe initiation system of the invention, it is evident that theinitiation system of the invention can reveal high sensitivity by thejoint use of the sensitizing dye and the activator compound. Inaddition, it is noted from Examples 1 to 6 that with respect to theactivator compound of the invention, a wide range can be appliedregardless of the sensitization mechanism thereof.

Examples 17 to 24 and Comparative Example 4

Lithographic printing plates were prepared in the following proceduresand evaluated for printing performance. The results are shown in Table2.

(Pre-Treatment of Support)

The surface of an aluminum plate (material quality: 1S) having athickness of 0.3 mm was sand blasted by using a No. 8 nylon brush and anaqueous suspension of 800-mesh pamiston and then thoroughly washed withwater. The resulting aluminum plate was dipped in and etched with 10% byweight sodium hydroxide at 70° C. for 60 seconds, washed with runningwater, neutralized and washed with 20% by weight nitric acid, and thenwashed with water. The aluminum plate was subjected to an electrolyticroughing treatment in a quantity of electricity at the time of anode of300 coulombs/dm² in a 1% by weight nitric acid aqueous solution using analternating waveform current of sine wave under a condition at a VA of12.7 V. A surface roughness thereof was measured and found to be 0.45 μm(in terms of an Ra expression according to JIS B0601).

(Hydrophilic Treatment of Support Surface)

The foregoing support was dipped in an aqueous solution containing 2.5%by weight of No. 3 sodium silicate (SiO₂: 28 to 30%, Na₂O: 9 to 10%, Fe:not more than 0.02%) having a pH of 11.2 at 70° C. for 13 seconds andsubsequently washed with water. A quantity of silicate on the surface asdetermined from the amount of Si element by fluorescent X ray analysisof the surface was found to be 10 mg/M².

(Coating of Interlayer)

A coating solution having the following composition (A) was prepared,coated on the surface of the foregoing support which had been subjectedto a hydrophilic treatment in a coating amount of phenylphosphonic acidof 20 mg/m² by using a wheeler at 180 rpm, and then dried at 80° C. for30 seconds.

(Coating Solution A for Interlayer)

Phenylphosphonic acid: 0.07 to 1.4 g Methanol: 200 g(Coating of Photosensitive Layer)

A photosensitive solution having the following composition was prepared,coated on the foregoing support having an interlayer provided thereon ina coating amount of from 1.0 to 2.0 g/m² by using a wheeler, and thendried at 100° C. for one minute.

(Photosensitive Solution)

Addition polymerizable compound 2.0 g (compound as described in Table2): Binder polymer (compound as described in 2.0 g Table 2): Sensitizingdye (compound as described in 0.15 g Table 2) Activator compound(compound as described 0.15 g in Table 2) Cosensitizer (C-2): 0.2 gColoring pigment dispersion 2.0 g (Composition of pigment dispersion)Pigment Blue 15:6 15 parts by weight Allyl methacrylate/methacrylic acidcopolymer 10 parts by weight (copolymerization ratio: 83/17):Cyclohexanone: 15 parts by weight Methoxypropyl acetate: 20 parts byweight Propylene glycol monomethyl ether: 40 parts by weight Thermalpolymerization inhibitor 0.01 g (N-nitrosophenylhydroxylamine aluminumsalt): Surfactant (MEGAFAC F-177, manufactured by 0.02 g Dainippon Inkand Chemicals, Incorporated): Methyl ethyl ketone: 20.0 g Propyleneglycol monomethyl ether: 20.0 g(Coating of Protective Layer)

A 3% by weight aqueous solution of polyvinyl alcohol (degree ofhydrolysis: 98% by mole, degree of polymerization: 550) was coated onthis photosensitive layer such that a coating weight after drying was 2g/m² and then dried at 100° C. for 2 minutes.

(Exposure of Lithographic Printing Plate Precursor)

The thus obtained lithographic printing plate precursor was subjected tosolid image exposure and halftone dot image exposure with 175 lines/inchfrom 1 to 99% at an interval of 1% by using monochromic light of 400 nmas a light source while adjusting an exposure power such that anexposure energy density on the plate surface became 200 μJ/cm².

(Development/Plate Making)

A prescribed developing solution (as described in Table 2) and afinisher FP-2W, manufactured by Fuji Photo Film Co., Ltd. were chargedin an automatic processor LP-850, manufactured by Fuji Photo Film Co.,Ltd., and the exposed plate was subjected to development and platemaking under a condition at a temperature of the developing solution of30° C. for a development time of 18 seconds, thereby obtaining alithographic printing plate.

(Printing Resistance Test)

Roland's R201 was used as a printing machine, and GEOS-G(N),manufactured by Dainippon Ink and Chemicals, Incorporated was used as anink. A printed matter in a solid image area was observed, and theprinting resistance was examined by the number of sheets at which theimage started to become faint. The larger the numerical value, thebetter the printing resistance is.

(Forced Halftone Dot Printing Resistance Test)

Roland's R201 was used as a printing machine, and GEOS-G(N),manufactured by Dainippon Ink and Chemicals Incorporated was used as anink. After printing 5,000 sheets, a PS plate cleaner CL-2, manufacturedby Fuji Photo Film Co., Ltd was infiltrated into a sponge for printing,a halftone dot portion was wiped by the sponge, and the ink on the platesurface was rinsed. Thereafter, 10,000 sheets were printed, and thepresence or absence of print spots of halftone dots in the printedmatter was visually observed.

(Staining Resistance Test)

Roland's R201 was used as a printing machine, and GEOS-G(S),manufactured by Dainippon Ink and Chemicals, Incorporated was used as anink. A printed matter in a non-image area (unexposed are) was observed,and the staining resistance was evaluated.

(Addition Polymerizable Compound in Table 2)

(M-1)

Pentaerythritol tetraacrylate (NK ESTER A-TMMT, manufactured byShin-Nakamura Chemical Co., Ltd.)

(Binder Polymer in Table 2)(B-1)

Allyl methacrylate/methacrylic arid/N-isopropyl acrylamide copolymer(copolymerization molar ratio: 67/14/19)

Measured acid value as determined by NaOH titration; 1.13 meq/g

Weight average molecular weight as determined by GPC measurement:130,000

(B-2)

Allyl methacrylate/methacrylic acid copolymer (copolymerization molarratio: 83/17)

Measured acid value as determined by NaOH titration: 1.55 meq/g

Weight average molecular weight as determined by GPC measurement;125,000

(B-3)

Polyurethane resin as a polycondensate of the following diisocyanatesand diols:

4,4′-Diphenylmethane diisocyanate (MDI)

Hexamethylene diisocyanate (HMDI)

Polypropylene glycol, weight average molecular weight: 1,000 (PPG1000)

2,2-Bis(hydroxymethyl)propionic acid (DMPA)/tetraethylene glycol (TEG)

Copolymerization molar ratio:(MDI/HMDI/PPG1000/DMPA/TEG)=40/10/11/26/13

Measured acid value as determined by KOH titration: 50.5 mg-KOH/g

Weight average molecular weight as determined by GPC measurement: 65,000

(Developing Solution in Table 2)

(DV-1) Aqueous solution comprising the following composition and havinga pH of 10: Monoethanolamine:  0.1 part by weight Triethanolamine:  1.5parts by weight Compound represented by the following formula 2:  4.0parts by weight Compound represented by the following formula 3:  2.5parts by weight Compound represented by the following formula 4:  0.2parts by weight Water: 91.7 parts by weight (DV-2) Aqueous solutioncomprising the following composition and having a pH of 10: Sodiumhydrogencarbonate:  1.2 parts by weight Sodium carbonate:  0.8 parts byweight Compound represented by the following formula 2:  3.0 parts byweight Compound represented by the following formula 3:  2.0 parts byweight Compound represented by the following formula 4:  0.2 parts byweight Water: 92.8 parts by weight (DV-3) Aqueous solution comprisingthe following composition and having a pH of 13: 1K potassium silicate: 3.0 parts by weight Potassium hydroxide:  1.5 parts by weight Compoundrepresented by the following formula 4:  0.2 parts by weight Water: 95.3parts by weight

Here, R represents H or C₄H₉; and n is about 4 (mean value).

Aqueous solution comprising the following composition and having a pH of12.0;

Potassium hydroxide: 0.2 g 1K potassium silicate (SiO₂/K₂O = 1.9): 2.4 gCompound represented by the foregoing formula 1: 5.0 g Tetrasodiumethylenediaminetetraacetate: 0.1 g Water: 91.3 g 

TABLE 2 Printing performance Photosensitive layer Composition PrintingPrinting Staining Addition Coating of resistance of resistance ofresistance of polymerizable Binder Sensitizing Activator amountdeveloping image area halftone dot non-image No. compound polymer dyecompound (mg/m²) solution (sheets) portion area Example 17 M-1 B-1 D2 A-1 1.4 DV-4 75000 Good Good Example 18 M-1 B-2 D13 A-2 1.4 DV-1 60000Good Good Example 19 M-2 B-3 D27 A-2 1.4 DV-4 100000 Good Good Example20 M-3 B-3 D12 A-2 1.1 DV-4 125000 Good Good Example 21 M-1 B-1 D4  A-21.4 DV-2 80500 Good Good Example 22 M-2 B-3 D5  A-1 1.4 DV-3 105000 GoodGood Example 23 M-3 B-3 D17 A-2 1.2 DV-4 112000 Good Good Example 24 M-2B-2 D14 A-1 1.4 DV-4 55000 Good Good Comparative M-1 B-1 Nil A-1 1.4DV-4 Image flew Image flew Good Example 4 out. out.

As is clear from Table 2, the lithographic printing plate precursorcontaining the photosensitive composition of the invention provideexcellent lithographic printing plates under conditions under whichplate making can be carried out with high producibility by scanexposure, namely under exposure conditions with very low energy. On theother hand, in Comparative Example 4 not using the initiation system ofthe invention, a practically useful lithographic printing plate was notobtained.

Example 25

A lithographic printing plate precursor was prepared in the same manneras in Examples 1 to 16, except that the initiation system was changed tothe following composition and that the film thickness of thephotosensitive layer was changed to 1.5 g/m².

Initiation system: D29: 0.10 g A-1: 0.15 g Cosensitizer: C-2:  0.2 g

The resulting lithographic printing plate precursor was subjected toscan exposure by using monochromic light of 400 nm under a conditionsuch that the exposure energy density was 0.25 mJ/cm². Next, the platewas heated at 100° C. for 10 seconds and then subjected to the foregoingdevelopment treatment.

There was thus obtained a lithographic printing plate having excellentvisibility and having a bluish green image. The resulting plate wassubjected to offset printing by using a Heidelberg's KOR-D machine. As aresult, more than 40,000 sheets of printed matters having excellentimage density and staining resistance could be obtained.

Example 26

The plate of Example 25 was exposed under a yellow lamp for one hourprior to exposure and then subjected to plate making and printing in theexactly same manner. Good results exactly the same as in Example 25 wereobtained.

Example 27

The plate of Example 25 was stored under a force storage condition at ahumidity of 65% and at a temperature of 45° C. for 3 days and thensubjected to plate making and printing in the exactly same manner. Goodresults exactly the same as in Example 25 were obtained.

Example 28

A photosensitive layer having the following composition was coated in acoating amount of 2.0 g/m² on a PET film.

(Contents in the Whole of Solids of Photosensitive Layer)

Binder resin (polymethyl methacrylate): 90.5% by weight  Sensitizing dye(the foregoing Illustrative Compound 2.0% by weight D-24): Activatorcompound A-6: 5.5% by weight Acid discoloring dye (naphthalenesulfonateof Victoria 2.0% by weight Pure Blue):

The resulting bluish green photographic material was exposed for 30seconds by using a metal halide lamp. The bluish green color wascompletely discolored, whereby the photographic material was changed toa pale yellow transparent film. In this way, the present initiationsystem also functions as an acid generator.

Example 29

The same operation as in Example 28 was followed, except for changingthe activator compound to A-7. The same light discoloration of the dyeas in Example 25 was acknowledged.

The same operation as in Example 28 was followed, except for changingthe activator compound to A-8. Light discoloration of the dye wasacknowledged.

The structures of the compounds in the Examples and Comparative Examplesother that the sensitizing dyes and the compounds of the formulae 1 to 4of the invention are as follows.

Here, Ts represents a tosyl group.

This application is based on Japanese Patent application JP 2004-221500,filed Jul. 29, 2004, the entire content of which is hereby incorporatedby reference, the same as if set forth at length.

1. A photosensitive composition comprising: a sensitizing dye represented by the following formula (1):

in which A represents an optionally substituted aromatic ring or an optionally substituted hetero ring; X represents an oxygen atom; and R₁, R₂, R₃, R₄, R₅, and R₆ each independently represents a hydrogen atom or a monovalent non-metal atomic group; an activator compound being capable of causing a chemical change due to a mutual action with light absorption of the sensitizing dye represented by the formula (1) so as to generate at least one of a radical, an acid and a base; and a compound being capable of reacting with at least one of a radical and an acid so that physical or chemical characteristics thereof change irreversibly.
 2. The photosensitive composition according to claim 1, wherein the activator compound is a titanocene compound.
 3. The photosensitive composition according to claim 1, wherein the compound being capable of reacting with at least one of a radical and an acid is an addition polymerizable compound having an ethylenically unsaturated double bond.
 4. The photosensitive composition according to claim 3, wherein the addition polymerizable compound has at least one terminal ethylenically unsaturated double bond.
 5. The photosensitive composition according to claim 3, wherein the addition polymerizable compound has at least two terminal ethylenically unsaturated double bonds.
 6. The photosensitive composition according to claim 1, further comprising a cosensitizer.
 7. The photosensitive composition according to claim 1, further comprising a thermal polymerization inhibitor.
 8. The photosensitive composition according to claim 1, wherein A in the formula (1) represents an optionally substituted N,N-diphenylaminobenzene group or an optionally substituted carbazole group.
 9. A lithographic printing plate precursor comprising a support and photosensitive layer containing the photosensitive composition according to claim
 1. 10. The lithographic printing plate precursor according to claim 9, wherein the photosensitive layer further contains a binder polymer.
 11. The lithographic printing plate precursor according to claim 9, further comprising a protective layer containing a water-soluble polymer so that the support, the photosensitive layer and the protective layer are in this order. 